Wednesday, 12 March 2014

Road Works General Specifications

A. Concrete

  • Max allowable temp for all types of concrete is 32 0 c.
  • Max allowable fall of pouring 1st 1.2 mts.
  • Max allowable slump 100+- 25 mm, water adding should not be allowed.
  • Max allowable time is 2hrs after batching
  • Normally ‘opc’ used for structural & src used for sub structures.
  • Normally types of mix a.40/20, b.30/20, c.25/20, d 20/20.: where ’40’ is compressive strength & 20 is the site of agg.

B. Wet mix

  • Minimum cbr should be 80 @ 100 % compaction.

C. Road base

  • Normally moisture content should be in between 4.5% to 6.5%.
  • Normal grading 70% agg (size = 5mm down) & 30% sand.
  • Agg used in wet mix : crushed & in road base natural.
  • Minimum compaction required is 98%

D. Prime coat

  • Average rate of application should be 0.8 to 1.2 kgs/sqm.
  • Temperature should be in between 600 c to 900 c curing time 48hrs.
  • Cut back asphalt mc =medium curing rc=rapid curing = sc=slow curing.

E. Tack coat

  • Average rate of application should be 0.15 to 0.35 kgs/sqm.
  • Temperature should be in between 100 c to 600 c.
  • Tack coat should be sprayed min 2hrs before laying aspahlt

G. Tiles

  1. Inter locking paving blocks:6cm thick for footpath:8cm for parking.
  2. Typical cross section shows:15cm=sub base,5cm coarse sand,6cm=tiles.
  3. First compaction after paving tiles,final after sand spreading..

H. Kerb stone

  1. Types upstand kerb,drop kerb,heel kerb,flush kerb(dimension varies)
  2. Fixing g.l.compacted 7cm con blind.fixed by mortar ,15cm con haunching.
  3. Pointing gap should be 4mm expansion joint should be at very 10mc.

I. Ducts

  1. All the services should be below 90cm from the frl(finish road level)
  2. Less than 90cm below frl,should be protected concrete production.
  3. Normal use :future or spare ductsplit duct,proposed duct
  4. Normally pvc & upvc pipes used for ducts,dla from 100mm to as required.
  5. Pipe lines :water =30cm to 60cm a/c irrigation =28cm pvc storm water=225mm .
  6. Mentral test & pressure tests conducted to confirm clear & lekage
  7. Test pressure shall be 1, 5 times the max working pressure & bar .
  8. Ducts above speci level shall be bedded & surrounded with 150mm con 15//20 .
  9. During backfill warning tape shall be installed over buried pipes.
  10. All ducts shall be provided std color drancord & std duct markers.
  11. Trench backfill shall be with appr mat & in 15cm compacted layers.

J. Safety measures:

  1. Trenches more than 1m deep shall protected with sheet piles (shoring) .
  2. Construction site should secured with cones, barrier & waring tapes.
  3. Temporary diversion sign boards, flash lights, should be installed.

K. Test a/c

  1. Marshal test (for stablity, flow, stifness, vim, vfb, vma) & core test (comp).
  2. Test for agg grading in asphalt also to find out bitumen content.(e/w)
  3. Mdd againest omc (proctor test) cbr field density (com) tests

L. Concrete

  1. Slump (workablity) test, test for compressive strength (by cubes).
  2. Paving blocks & kerb stones shall be tested for crushing value.

F. Asphalt

  1. Is a mixture of coarse aggregate, fine aggregate filler material & bitumen binder.
  2. Mix types /dense mix &stiff mix grad a.40/50 & b,60/70.
  3. Normal asphaltic layer thickness/b.c=80mm bi.c=60mm w.c =40mm.
  4. Normal aggregate/ Base Course =37mm & down binder .c=25mm & down wearing c =19mm & down.
  5. Required min compaction /b.c=97: bi c=97: w.c=98%.
  6. If compaction is more than 101.8% the asphalt should be rejected
  7. Allowable temp in asphalt

    1. surface temp before laying =18 0 min
    2. batching temp=1630c max
    3. laying temp=1350 c to 1630 min & max
    4. breakdown temp=1200 to 1400 c
    5. temp in joints should be 900 c min.
  8. In logitudinal joints 15cm over lap should be maintained.
  9. All logitudinal & transverse joints should cut vertical.
  10. Asphalt laying & rolling should be done from lower to upper.
  11. Asphalt should be laid max 1.50 m to get req tem in joints.
  12. Modified asphalt to increase stiffness 10 to 15% of chemcrete is mixed with bitumen while batching also to increase stability.
  13. Bleeding surface flow of bitumen (occurs due to over spray of tack coat) by placing hot mix over sprayed should be removed.
  14. Segregation / accumulation of agg. should replaced with fine mix
  15. To know no of passes required for of min comp, trail area 30mt to be prepared.
  16. Inspector to check during asphalt, segregation open texture tearing action using straight edge constantly, & tem regularly.
  17. Pot holes: less asphalt thin asphalt surface, poor drainage & ponding due to oil & diesel patches slippage cracks with form.
  18. Cracks can be repaired by, bitu- sealant, hot mix asphalt emulsion slurry.
  19. Camber = two side slope (nor1.5%) cross fall=one side slope(nor2%)
  20. In long & tran joints between layers 15cm offset is kept for good comp.
  21. While asphalt paving the speed of paver should be 4 to 6 km/min.
  22. Weight of STR (Steel Tandom Roller) should be in between 8 to 12 ton.
  23. Weight of PTR (Pneumatic Tyre Roller) should be 20 to 25 ton/ tyre pressure should be in between 6 to 6.3 kg/sqcm or 80 to 110 psi/
  24. Rollers speed should 5km/hr, should maintain overlap in passes/
  25. Staggered rolling should be done in passes, to avoid channeling/
  26. First & final rolling should be with STR & in middle with PTR.
  27. First to seal temp, final for smooth finish, PTR for inform comp.
  28. Veg oil lubrication used on PTR tyre ,should not be excess.
  29. While rolling at super elevation drive wheel should be forwarded, to avoid pushing of material.
  30. After 24 hrs re rolling is avoided design period will be reduced.
  31. Traffic should not be allowed min 7 days on fresh asphalt pavement.
  32. Transverse joints should be in min 50cm offsets for each line.
  33. FRL(finish road level) should be 15cm below the kerb stone
  34. Normal widths c.w=6m 7.3m & 11.5m p.p =2.5m d.p =5.5m s.w.=2.5m:mn=3m.
  35. Prime coat is sprayed over wet mix to seal the moisture content.
  36. Asphalt should layer 25% more to get req thickness after compaction.
  37. String line supported 10m interval pegs to get uniform levels.
  38. Joints should cut verticaly(900) toget proper compaction in joints.
  39. Asphalt leveling at joints should done careful to avoid jump & sag.

M. Miscellaneous

  1. Embankment should be in 15cm compacted layers approved material.
  2. CBR of exist mat should be 15.at formation level.
  3. Formation level should be compacted 95% and CBR should be 15%.
  4. Improved sub grade should be compacted 95% and CBR should be 30.
  5. Use of saline water. Should be avoided in Construction & compaction works.
  6. Before executing job trial trench's or pits to be excavated to find existing service.
  7. Construction area shall be checked with cable detector to locate the exist cables.
  8. Reference point for all levels shall be taken from standard bench mark.
  9. For trench where water table is high dewatering pump shall be used.
  10. Before laying pipe lines, 15cm sand bedding should be layed.
  11. Curing shall be done for min 7 days for all concrete work.
  12. For emergencies curing compound is allowed to proceed for further job.
  13. 25 mm grouting shall be done for base of storm water manhole.
  14. GRP liner shall be provided for all sewer manholes.
  15. Rock fill layer is used in road const, where the water table is high.

M. Equipment

  1. Earth work= grader, showel, back hoe, static roller & vibrator roller.
  2. Asphalt works= Paver, STR (Steel Tandom Roller) PTR (Pnuematic Tyre Roller).
  3. Others: transit mixer, spray tanker, bob cat, dumber, baby roller.
  4. Equipment used in asphalt should be without leakage of oil & diesel.
  5. All const works shall execute under: std spec limits & tolerances.

How GRC (Glass fiber Reinforced Concrete) is casting?

G.R.C:Glass reinforced concrete, sometime referred as G.F.R.C. (Glass fiber Reinforced Concrete) it is Cement based civil construction material, mainly for decoration purpose to form the architectural shape of structure manufacture to the hand-spray process or pre-mix, mainly with:
• White cement (O.P.C)
• Silica sand.
• Alkali resistant Glass fiber.
• Water.
• Admixture.
• Plasticizer-polymer.
• Pigments.
• Others-Marble chips, Mirror glaze chips etc.


METHODS 

  1. Direct spray: started by weighing (using calibrated weighing equipment) than mixing (using a high shear mixer), Spraying using specialist equipment allowing the simultaneous deposition of known quantities of cementious slurry and chopped glass fiber.
  2. Premix vibration casting: started by weighing then mixing, pouring the materials in the mould parallel with the vibrating method shall ensure the filling is such that air is expelled from the product and planes of weakness are avoided.
  • MOULD: As a first stage mould is prepared to the required element to its exact size and shape in steel, timber, G.R.P (Glass reinforced plastic), rubber or in other material based on the shape and size of the product.
  • Casting:The method of casting is with hand spray process. A facing layer of white cement, pigment, silica sand (with required marble or glaze chip if required according to the texture) water and acrylic Polymer is sprayed on to the mould without fiber and then left to harden slightly (not to set). The facing layer is normally 1.5 to 2.5 m.m thick and G.R.Cis then sprayed in to this to the required thickness of normally 9-19m.m based on size and design of element. If the G.R.Cpanel require (for big panels only) the stiffeners, pre-cut polystyrene pads in required profile shape is positioned and again G.R.C is sprayed to form the box type stiffeners to a minimum thickness of 10 to 15 mm . After the initial settings and after demolding keep it up to final setting time and dispatch to site if it is white smooth finish or pigmented smooth finish.
  • STONE FINISH After de-molding the face of panel is washed with hydrochloric acid until the required texture is achieved. Brushing on the acid and scrubbing the panel with a stiff brush. Other way the face of whole panel shall be dipped in to a large acid bath. Prior to delivery to site a final wash with dilute acid in normally applied to remove efflorescence (white staining), which may have occurred. Then finally wash with pure water. (Acid, use HYDROCLORICACID diluted 1 part 3 to 4 parts water or required proportion).
  • ADMIXTURE "CHROMIX"admixture for color conditioned concrete manufacture by Mis L.M.SCOFIELD EUROPELTD, U.K.
  • GLASS FIBER ALKALI RESISTANT glass fiber from EUROPE or JAPAN.
More Products

G.R.C finishing

There are three groups:
a) G.R.C White smooth finish: - After installation in its place, it shall be painted to required color and texture quality paints. Preferably epoxy based paint.
b) G.R.C Color -pigmented -smooth finish:Pigmented G.R.C not required Paint or it can be painted also later.
c) G.R.C Stone finish &acid washed:This will give rough or fair rough stone finish appearance. It is not required any further painting or finishing. It shall be a unique single color and pattern.

FIXING

Generally all solid panels to external facades of buildings and villas with their different sizeas shown in the shop drawings are provided with cast in steel channels (2SxSOx1.7mm) all around the panels. According to design and size, the G.R.C panels are also provided vertically and horizontally with G.R.C stiffeners (at back side), to strengthen Them G.R.C panels should be fixed on concrete surface (not on hollow block wall).
Panels are fixed through steel frame to concrete, with threaded bar (lOx120 mm), nuts, washers and expoxy.
As for G.R.C Pergolas, the G.R.C rafters will be reinforced with 4nos of steel bars (dia=14mm). Some panels required angle brackets (7Sx7Sx7Sx10mm). These angles will be fixed to concrete with anchor bolt (12 mm).

Wednesday, 26 February 2014

Flow table test

The flow table test or flow test is a method to determine the consistence of fresh concrete.
Application When fresh concrete is delivered to a site by a truck mixer it is sometimes necessary to check its consistence before pouring it into formwork.
If the consistence is not correct, the concrete will not have the desired qualities once it has set, particularly the desired strength. If the concrete is too pasty, it may result in cavities within the concrete which leads to corrosion of the rebar, eventually leading to the formation of cracks (as the rebar expands as it corrodes) which will accelerate the whole process, rather like insufficient concrete cover. Cavities will also lower the stress the concrete is able to support.

Equipment

Flow table with a grip and a hinge, 70 centimeters (28 in) square.
Abrams cone, open at the top and at the bottom - 30 centimeters (12 in) high, 17 centimeters (6.7 in) top diameter, 25 centimeters (9.8 in) base diameter.
Water bucket and broom for wetting the flow table.
Tamping rod, 60 centimeters (24 in) long

Conducting the test

  • The flow-table is wetted.
  • The cone is placed in the center of the flowtable and filled with fresh concrete in two equal layers layers. Each layer is tamped 10 times with tamping rod.
Wait 30 seconds before lifting the cone
  • The cone is lifted, allowing the concrete to flow.
  • The flowtable is then lifted up 40mm and then dropped 15 times, causing the concrete to flow
  • After this the diameter of the concrete is measured.

Monday, 24 February 2014

DMS Force Measuring Unit


for testing single-wire stressing jacks, for force measurement on casting beds, with or without extension piece The DMS Force Measuring Unit provides for the measurement, monitoring and checking of the tension applied to wires and strands and for the six-monthly testing of stressing jacks in accordance with DIN 1045-1 and DIN 51308. The DMS Force Measuring Unit comprises a precision force transducer with center hole to which straingauge strips are cemented, a measuring amplifi er and all the centering and receiving elements and discs needed for the testing of stressing jacks and for the measurement of the forces applied on prestressing beds. It is suitable for use with anchor barrel diameters of 20.5 to 60 mm. For force measurements to be made on prestressing beds additional support pieces and intermediate pieces as detailed in leafl et 81-200 Bl.1 are needed. For the routine testing of stressing jacks, intermediate pieces as detailed in leafl et 81-200 Bl.1 are also needed. The force transducer is connected to the measuring amplifi er via a 2.0 m long cable with a multi-pin socket. This socket can also be used for connecting a PAUL Strain Gauge Head as described in leafl et B 101.12/1. An offi cial calibration certifi cate is available at an extra charge. Recalibration every 2 years.
Force transmitting elements included in the scope of supply:
1 Receiving element (13-311.13)
1 Centering element (13-311.07)
1 Sleeve (13-311.09)
1 Set of centering discs D5.5 - D16 (see selection table)
1 Anchor grip receiving element (13-311.08)

Technical Data
Rated load: 200 kN and 500 kN
Accuracy: +/- 0.5%
Display: 10 daN
Power supply (battery): 2.5 VDC / 30 mA
Dimensions of force
transducer: see Fig. 2
Dimensions of case: 450 x 350 x 80 mm
Weight complete: 7.5 kg

Friday, 21 February 2014

Expanded polystyrene (EPS) for Thermal Insulation

Expanded Polystyrene (EPS) is produced from styrene monomer, derivative of ethylene and Benzene by applying polymerization process.
Expanded polystyrene foam (EPF) is a plastic material that has special properties due to its structure. Composed of individual cells of low density polystyrene, EPF is extraordinarily light and can support many times its own weight in water. Because its cells are not interconnected, heat cannot travel through EPF easily, so it is a great insulator. EPF is used in flotation devices, insulation, egg cartons, flats for meat and produce, sandwich and hamburger boxes, coffee cups, plates, peanut packaging, and picnic coolers. Although it is generally called Styrofoam, Styrofoam is a trademark of Dow Chemical Company and refers specifically to a type of hard, blue EPF used mainly in boating.
Expanded Polystyrene
 Foam Sheets,
4" x 24" x 48", qty 1
EPS's main component is styrene (C 8 H 8 ), which is derived from petroleum or natural gas. Styrene is polymerized by heat. Stopping the polymerization is difficult; however, inhibitors such as oxygen, sulfur, or quinol can be used. To form the low-density, loosely attached cells EPF is noted for, polystyrene must first be suspended in water to form droplets. A suspension agent, such as specially precipitated barium sulfate or copolymers of acrylic and methacrylic acid and their esters (organic product formed by the reaction between of an acid and an alcohol), is then added to the water. Numerous suspension agents are used commercially. All are similarly viscous and serve to hold up the droplets, preventing them from sticking together. The beads of polystyrene produced by suspension polymerization are tiny and hard. To make them expand, special blowing agents are used, including propane, pentane, methylene chloride, and the chlorofluorocarbons.
First, styrene is made by styerenemonomer. Next, the styrene is subjected to suspension polymerization and treated with a polymerization initiator, which together convert it into polystyrene. Once a polymer chain of the desired length has formed, technicians stop the reaction with terminating agents. The resulting polystyrene beads are then cleaned, and anomalous beads filtered out. To make small-cell EPF, workers then melt, add a blowing agent to, and extrude the beads. To produce smooth-skinned EPF, they pre-expand the beads, dramatically reducing their density. Next they heat and expand them before allowing them to sit for 24 hours so that they can cool and harden. The beads are then fed into a mold of the desired shape.

Expanded polystyrene blocks, boards or injection moulded products conform to BS 3837: 1977 and are available in two grades i.e. Type N & Type A. Type N is the standard while its modified version by the incorporation of flame retardant additives. -the Type A meets the additional requirement for the extent of burn when tested in accordance with BS 4735.
Characteristics of Expanded Polystyrene: High thermal insulation value. Resistance to decay, age and water. Low water vapour transmission. Rigid but extremely light in weight

APPLICATIONS

  • Expanded polystyrene as thermal insulation and impact noise insulation - is the most efficient material used in the building industry for insulating walls, floors, ceilings, roofs etc.
  • It's also used in the building as expansion joints filler, as permanent concrete filler and in sandwich panels for the pre-fabrication filed etc.
  • As ceiling tiles, besides its insulating power, expanded polystyrene have an attractive appearance.
  • It's the most widely used insulation for refrigerated rooms, freezers, trucks, piping, air ducting.
  • Expanded Polystyrene, due to its negligible weight, has great buoyancy and with its rigidity and impermeability it has become widely used in the flotation field under various forms and shapes.
  • Because of its advantageous characteristics, its nice appearance and particularly its impact absorbing properties expanded polystyrene has become the ideal packaging material.
  • Expanded Polystyrene is much used for decorative works because of its low density and easy workability it keeps suggesting new applications to those who work with it

ADVANTAGES

  • Cutting and shaping of expanded polystyrene is extremely easy. It can be cut with ordinary wood or metal saws, with a fine blade especially with hot wire which produces exceptionally smooth cut surfaces.
  • Expanded Polystyrene will adhere to itself or to a wide variety of materials through the use of adhesives containing other than petroleum-derived solvents.
  • Expanded Polystyrene can easily be painted but only with latex, water of epoxy paints

Benefits

Insulate & Weatherize:
For Energy Efficiency at Home

  • Good energy saver.
  • Save money up to 40%
  • Hygienic, free from fungus and germs etc.
  • Create comfortable living and working environment.
  • One time investment and life long benefit.
  • Protects household from heat and cold

Features

  • Excellent thermal insulation.
  • High resistance to water absorption.
  • Good resistance to moisture.
  • High compressive strength and flexural strength.
  • Resistance to all climates.
  • Very strong, easy to cut and handle.
  • Protect heat, cold and resistant to most of the chemicals.
  • Good water proofing membranes.
  • No harm to human body, animals and plants.
  • Economic compared with other insulation materials.
  • Environment friendly.

Environment impact factor ODP, CFC & GWP

The Visual Handbook
of Energy Conservation:
A Comprehensive Guide 

to Reducing Energy Use at Home
Ozone Depletion Potential (ODP) is the potential of any gas to deplete the ozone layer. Expandable Polystyrene (EPS) uses Pentane as its blowing agent. Pentane has an ODPof ZERO. Therefore the ODP value of EPS is ZERO.
Expanded Polystyrene is HFC, CFC, and HCFC, free since it has no chlorine content.
Global Warming Potential (GWP) is a method of measuring the strength of different 'greenhouse' gases in the atmosphere and used to define the impact on global warming over different periods of time. C02 has a GWP of J over 100 years. HFC, CFC, HCFC and methane arc measured relative to C02, their relative global warming effect after 100 years relative to the simultaneous emission of the same mass of C02. EPS has a GWP<5 when measured relative to CO2 over 100 years.

Thursday, 20 February 2014

Bleeding in Concrete -Causes, effects, and control

Introduction

Bleeding of concrete is always not bad. It helps to lower the w/c ratio and helps to densify the concrete. But the bleeding concrete can cause a number of problems like pumpline jams, sand streaks in walls, weak horizontal construction joints, and voids beneath rebars and aggregate particles. Even if bleeding isn’t excessive, finishing concrete at the wrong time causes a different set of bleeding-related problems: blistering, scaling, and dusting surfaces.
A thorough knowledge of why concrete bleeds and how mix proportions affect it, is required to preventing the harmful effects of bleeding. Adoption of right finishing methods also helps to ensure that the bleeding problems won’t ruin a slab surface.

The Concrete Bleeding process

Almost all freshly placed concrete, water oozes out to the surface as bleed water. As aggregate and cement particles settle, they force excess mixing water upward. The process continues until settlement stops, either because of solids bridging or because the concrete has set.
The total amount of bleeding or settlement depends on mix properties, primarily water content and amount of fines (cement, fly ash, fine sand). Increasing water content increases the bleed-water, and increasing the amount of fines reduces bleeding. Amount of bleeding is also proportional to the depth of concrete placed. More bleed-water rises in deep sections than in thin ones.
Bleeding usually occurs gradually by uniform seepage over the whole surface, but sometimes vertical channels form. Water flows fast enough in these channels to carry fine particles of cement and sand, leaving “wormholes” in the interior or sand streaks at the form face. Channels are more likely to form when concrete bleeds excessively.
Channels that reach the surface are open paths for deicing solutions to penetrate the concrete. This leads to freezing and thawing damage and rebar corrosion.
This comprehensive guide delivers the step by step methods to decorative concrete overlays. This amount of information can't be found anywhere else.
The Decorative Concrete Overlay business is an exploding new industry. When we say "new", we mean that it is just now catching the public eye. However, this process has actually existed for over thirty years. Decorative Concrete Overlays can dramatically enhance boring grey concrete into a wonderful works of art, or simply repair concrete that would have had to have been torn out and replaced. People are starting to see that not only can Decorative Concrete Overlays save them money, applying Decorative Concrete Overlays can also add curb appeal to their home.

Engineered Concrete Mix Design and Test Methods (Modern Concrete Technology Series)

Engineered Concrete Mix
Design and Test Methods
(Modern Concrete
Technology Series)

Mix Design and Test Methods helps engineers, as well as laboratory technicians, grasp a better understanding of Portland Cement and Portland Cement Concrete. The book is divided into several sections, with the first, Mix Design Procedures, explaining how concrete batches are designed, mixed, and measured for various consistencies. Another section details the tests of the primary component materials of concrete other than water - namely Portland Cement, aggregates, and mortar - while the final section includes some of the fundamental concrete testing procedures for different strength parameters in conformity with the standards of the American Society for Testing Materials.

Effects of excessive bleeding in deep sections

Concrete weathers and disintegrates most severely at the tops of walls, piers, and parapets. One reason for this is water gain that’s caused by bleeding. Sometimes bleed-water can’t entirely evaporate because it has been trapped near the top surface by setting. This raises the water-cement ratio, increases permeability, and lowers strength. The effect has been noted in laboratory load tests of full-sized columns where failure almost always was near the column top.
Excessive bleeding also causes some other problems in deep sections:
  • Heavy laitance accumulation at horizontal construction joints. This plus the higher water- cement ratio near the surface can cause a plane of weakness at the joint.
  • Bond loss at aggregate and rebar surfaces. Channels form at the surface of coarse aggregate particles (Figure 1) or water collects beneath rebars.
  • Unsightly sand streaks (Figure 2) caused by bleedwater rising at the form face. Concretes that bleed excessively can cause problems even before they’re placed. When these mixes are pumped, pressure in the pumpline forces water and cement in front of the concrete. With less paste to lubricate the line, rock jams form and the line plugs.

Bleeding problems in flatwork

Never float or trowel concrete while there’s bleedwater on the surface. That’s the cardinal rule of finishing. Strike off and bull float the concrete before bleeding begins, then wait for it to end and water to evaporate before finishing. Excessive bleeding causes excessive waiting by the finishers. Unless this water is removed, delays increase finishing costs. But getting on the concrete too soon reduces surface quality. Finishing before bleed-water has evaporated can cause dusting, craze cracking, scaling, and low wear resistance. Working bleed-water into the surface also increases permeability; water, deicing salts, and other harmful chemicals can enter the concrete more easily. Highly permeable concrete increases the possibility of rebar corrosion too. Floating or troweling concrete prematurely can cause surface defects even if there’s no bleed-water on the surface. Sealing the surface before bleeding stops traps bleed-water beneath the surface. Blisters may form (Figure 3), or the whole surface may peel off later because of a weak, very porous concrete layer beneath the sealed surface.
Be particularly careful to control mix variables that affect bleeding when concrete slabs will be placed on a nonabsorbent base or during cold weather. Plastic vapor barriers or tightly compacted clay soils beneath the slab aggravate bleeding problems (Figure 4). Because the base absorbs no water, more excess water comes to the surface.
Low temperatures prolong the bleeding period. A combination of cool concrete and rapidly drying surface in a heated enclosure can cause blistering or surface scaling.
If the concrete is already in place and bleeding too much, fans may speed evaporation and permit earlier finishing. Another solution is dragging a rubber hose slowly over the entire surface; concrete should be stiff enough so that only water is removed. In small areas, a single pass with the tilted edge of a trowel removes the excess water.
Figure 4. Plastic vapor barriers aggravate bleeding problems. Concrete on the left part of the slab is placed on a vapor barrier, concrete on the right on a granular base. Note the water sheen still present over the vapor barrier.
Figure 4. Plastic vapor barriers aggravate bleeding problems. Concrete on the left part of the slab is placed on a vapor barrier, concrete on the right on a granular base. Note the water sheen still present over the vapor barrier.


How to control bleeding

Excessive bleeding can be avoided. Don’t add too much water to the concrete. Most of the water added to make placing easier bleeds out of the concrete. Any time saved during placement will be lost while waiting for the bleedwater to evaporate. Place concrete at the lowest possible slump. If you need a higher slump to speed placement, consider using a superplasticizer. Add additional concrete fines to reduce bleeding. The fines may come from a number of sources:
  • Use a more finely ground cement. Concretes made with high early strength (Type III) cement bleed less because the cement is ground finer than normal (Type I) cement.
  • Use more cement. At the same water content, rich mixes bleed less than lean mixes.
  • Use fly ash or other pozzolans in the concrete.
  • If concrete sands don’t have much material passing the No. 50 and 100 sieves, blend in a fine blow sand at the batch plant.
  • For air- entrained concrete, use the maximum allowable amount of entrained air. Consider using an air- entraining agent whenever excessive bleeding is a problem. Entrained air bubbles act as additional fines. Air entrainment also lowers the amount of water needed to reach a desired slump. 

Concrete Mix Design Calculations- Water Cement Ratio and Optimum Cement Content and Ideal Aggregate Propotions

Mix Design C-40 Grade

This Concrete mix design C-40 grade is for reference purpose only. Actual site conditions vary and thus this should be adjusted as per the location and other factors.

Parameters for mix design C40

Grade Designation = C-40
Type of cement = O.P.C
Brand of cement = National
Admixture = Sodamco CF 100
Fine Aggregate = Zone-II
Sp. Gravity Cement = 3.15
Fine Aggregate = 2.61
Coarse Aggregate (20mm) = 2.65
Coarse Aggregate (10mm) = 2.66
Minimum Cement = 400 kg / m3
Maximum water cement ratio = 0.45

Mix Calculation: -

1. Target Mean Strength = 40 + (5 X 1.65) = 48.25 Mpa

2. Selection of water cement ratio:-
Assume water cement ratio = 0.4

3. Calculation of cement content: -
Assume cement content 400 kg / m3
(As per contract Minimum cement content 400 kg / m3)

4. Calculation of water: -
400 X 0.4 = 160 kg Which is less than 186 kg
Hence o.k.

5. Calculation for C.A. & F.A.:
V = [ W + (C/Sc) + (1/p) . (fa/Sfa) ] x (1/1000)

V = [ W + (C/Sc) + {1/(1-p)} . (ca/Sca) ] x (1/1000)

Where

V = absolute volume of fresh concrete, which is equal to gross volume (m3) minus the volume of entrapped air ,

W = mass of water ( kg ) per m3 of concrete ,

C = mass of cement ( kg ) per m3 of concrete ,

Sc = specific gravity of cement,

(p) = Ratio of fine aggregate to total aggregate by absolute volume ,

(fa) , (ca) = total mass of fine aggregate and coarse aggregate (kg) per m3 of
Concrete respectively, and

Sfa , Sca = specific gravities of saturated surface dry fine aggregate and Coarse aggregate respectively.

As per Table No. 3 , IS-10262, for 20mm maximum size entrapped air is 2% .

Assume F.A. by % of volume of total aggregate = 36.5 %

0.98 = [ 160 + ( 400 / 3.15 ) + ( 1 / 0.365 ) ( Fa / 2.61 )] ( 1 /1000 )

=> Fa = 660.2 kg

Say Fa = 660 kg.

0.98 = [ 160 + ( 400 / 3.15 ) + ( 1 / 0.635 ) ( Ca / 2.655 )] ( 1 /1000 )

=> Ca = 1168.37 kg.

Say Ca = 1168 kg.

Considering 20 mm : 10mm = 0.6 : 0.4

20mm = 701 kg .
10mm = 467 kg .

Hence Mix details per m3
Cement = 400 kg
Water = 160 kg
Fine aggregate = 660 kg
Coarse aggregate 20 mm = 701 kg
Coarse aggregate 10 mm = 467 kg
Admixture = 0.6 % by weight of cement = 2.4 kg.
Recron 3S = 900 gm

Water: cement: F.A.: C.A. = 0.4: 1: 1.65: 2.92

Observation: -
A. Mix was cohesive and homogeneous.
B. Slump = 110mm
C. No. of cube casted = 12 Nos.
7 days average compressive strength = 51.26 MPa.
28 days average compressive strength = 62.96 MPa which is greater than 48.25MPa

Hence the mix is accepted.

Mix Design C-50 Grade

The Concrete mix design C-50 grade (Using Admixture –Sikament) provided here is for reference purpose only. Actual site conditions vary and thus this should be adjusted as per the location and other factors.
Parameters for mix design M50

Grade Designation = C-50
Type of cement = O.P.C
Brand of cement = National Cement
Admixture = GIC SP 600
Fine Aggregate = Zone-II

Sp. Gravity
Cement = 3.15
Fine Aggregate = 2.61
Coarse Aggregate (20mm) = 2.65
Coarse Aggregate (10mm) = 2.66
Minimum Cement =400 kg / m3
Maximum water cement ratio = 0.45
Mix Calculation:
1. Target Mean Strength = 50 + ( 5 X 1.65 ) = 58.25 Mpa

2. Selection of water cement ratio:
Assume water cement ratio = 0.35
3. Calculation of water:
Approximate water content for 20mm max. Size of aggregate = 180 kg /m3. Usage of plasticizer will reduce water content by 20%.

Now water content = 180 X 0.8 = 144 kg /m3
4. Calculation of cement content:
Water cement ratio = 0.35
Water content per cum of concrete = 144 kg
Cement content = 144/0.35 = 411.4 kg / m3
Say cement content = 412 kg / m3

5. Calculation for C.A. & F.A.: [ Formula's can be seen in earlier posts]
Volume of concrete = 1 m3Volume of cement = 412 / ( 3.15 X 1000 ) = 0.1308 m3Volume of water = 144 / ( 1 X 1000 ) = 0.1440 m3
Volume of Admixture = 4.994 / (1.145 X 1000 ) = 0.0043 m3
Total weight of other materials except coarse aggregate = 0.1308 + 0.1440 +0.0043 = 0.2791 m3
Volume of coarse and fine aggregate = 1 – 0.2791 = 0.7209 m3
Volume of F.A. = 0.7209 X 0.33 = 0.2379 m3 (Assuming 33% by volume of total aggregate )
Volume of C.A. = 0.7209 – 0.2379 = 0.4830 m3Therefore weight of F.A. = 0.2379 X 2.61 X 1000 = 620.919 kg/ m3Say weight of F.A. = 621 kg/ m3Therefore weight of C.A. = 0.4830 X 2.655 X 1000 = 1282.365 kg/ m3Say weight of C.A. = 1284 kg/ m3Considering 20 mm: 10mm = 0.55: 0.45
20mm = 706 kg .
10mm = 578 kg .
Hence Mix details per m3Increasing cement, water, admixture by 2.5% for this trial

Cement = 412 X 1.025 = 422 kg
Water = 144 X 1.025 = 147.6 kg
Fine aggregate = 621 kg
Coarse aggregate 20 mm = 706 kg
Coarse aggregate 10 mm = 578 kg
Admixture = 1.2 % by weight of cement = 5.064 kg.

Water: cement: F.A.: C.A. = 0.35: 1: 1.472: 3.043
Observation:
A. Mix was cohesive and homogeneous.
B. Slump = 120 mm
C. No. of cube casted = 9 Nos.
7 days average compressive strength = 52.07 MPa.
28 days average compressive strength = 62.52 MPa which is greater than 58.25MPa Hence the mix accepted.

Monday, 5 December 2011

Methods of Manufacturing of GRC

Spraying

Spraying of fibre and slurry simultaneously onto a mould, by manual or mechanical means. Typical products made using the spray process include architectural cladding panels, channels, tanks, facade elements, ducting and permanent formwork.


Sprayed GRC

 In the manufacture of GRC by the spray process, simultaneous sprays of cement/sand mortar slurry and chopped Cem-FIL AR glass fibre are deposited from a spray-head into or onto a suitable mould. The spray-head may be hand held or mounted on a machine. The mortar slurry is fed to the spray gun from a metering pump unit and is broken into droplets by compressed air. Cem-FIL AR fibre roving is fed to a glass fibre chopper/feeder, mounted on the spray head which chops the fibre to predetermined lengths, typically 25-40 mm and injects the chopped strands into the mortar spray so that a uniform felt of fibre and mortar is deposited on the mould. The slurry has typically a sand:cement ratio of up to 1:1 and a water:cement ratio of 0.33.


The water:cement ratio should be kept as low as possible consistent with satisfactory spray and incorporation characteristics, as increasing the water:cement ratio leads to a reduction in the strength of the product. Admixtures may be used to obtain the required workability. The proportion of fibre to slurry is adjusted so that the resulting composite contains typically 5% by weight of glass fibre.


Manual Spray MethodThe operator holds the spray-head in his hand and moves it to and-from across the mould, directing the stream of material perpendicular to the mould surface, until the required thickness of GRC has been built up. Roller-compaction ensures compliance with the mould face, impregnation of the fibre by the slurry, removal of trapped air and development of adequate density. The rolled surface may be finally trowelled smooth. Thickness control is achieved by use of pin-gauges. A typical output of a single hand-unit is 10-12 kg of GRC per minute. The process results in one surface of the product having an ex-mould finish and the other surface a rolled or trowelled finish Products are covered with polythene sheet after spraying and normally demoulded the following day and then cured. The process is labour intensive but is capable of producing complex shapes and is extremely versatile. The process is used for manufacture of a wide range of components including cladding panels, agricultural components, facade elements, formwork and ducting.

During Spraying


Good quality Cem-FIL GRC is produced when there is a minimum of trapped air (low pressures, good compaction) and when the fibres are well distributed (correct percentage and good spray technique).
1. It is normal good practice to spray in layers (roughly 3-4 mm thick) at a speed likened to waltz-time.
2. Each layer should be compacted before the next layer is sprayed.
3. Each layer consists of spraying in alternate directions.


Premixing


Premixing the fibre and slurry and then processing the mixture by vibration casting, extrusion, injection moulding, etc., to produce the end product form. Typical products made using the premix process are sunscreens, planters, electrical transformer housings, slates and tiles, junction boxes and drainage components.

Premixed GRC

All premix processes involve the blending together of the cement, sand, water, admixtures and choppe d strands of Cem-FIL fibre in a mixer prior to being formed. To produce a premix of the correct quality it is necessary to mix in two stages. The first stage is designed to produce a high quality slurry to achieve the necessary workability and allow for the uniform incorporation of fibre. The second stage is the blending of fibres into the slurry at a reduced speed. It is more convenient to carry out both stages in the same piece of equipment, but separate mixers can be used for each stage. The actual mix formulation used depends upon the type of product being made, but a typical mix has a sand:cement ratio of 2:3 and a water:cement ratio of preferably less than 0.35. It is essential to keep the water:cement ratio as low as possible consistent with maintaining workability of the mix, so admixtures are used.

Up to 4% by weight of chopped strands can be incorporated into the mix, but typical fibre content is 3%. The fibre length is normally 12 mm because above this length the mix becomes difficult to work. A fibre length of 25 mm is generally found to be the maximum useable. Although the glass fibre strands are designed to withstand the mixing action, it is normal, as indicated above, to add the fibre at the end of the mixing cycle to minimise fibre damage.

Curing of GRC Products
The hydration of cement is a relatively slow process at ambient temperatures and for this reason concrete products are usually allowed to hydrate or ‘cure’ for several weeks after casting to give full strength development. GRC products are normally of comparatively thin section, manufactured with a lower water:cement ratio than most conventional concretes, and are prone to rapid drying. If this occurs before hydration is complete the cement never achieves its full strength and the properties of the GRC are adversely affected, so more attention to curing conditions is necessary.

Moist Curing of GRC Products


To ensure complete hydration it is essential that products are kept moist immediately after manufacture and during the curing period. Several methods of achieving this are currently in use, mainly: storage in a humidity chamber or fog room, sealing in polythene bags, or total immersion in water. For all products the curing period can be divided into three parts:

  1. A pre-demoulding cure to give sufficient strength to the product for demoulding. This is important and is carried out by covering the component closely with polythene to minimise air flow across the GRC surface thus enabling the component to retain as much water as possible.
  2. The main cure as described above.
  3. Post-curing during which the product is normalised to the ambient conditions prior to storage or use, particularly in extreme hot or cold conditions. The rate of hydration will be different in each of these periods, but at the end of the curing cycle the GRC should have been brought up to the final strength requirements. The particular curing regime will depend upon the product, manufacturing process and mix design, and must be such that the required level of properties is achieved. During the curing period the strength of the GRC products will be building up from an initially low level and care is necessary in demoulding, handling and particularly in the main cure to ensure that products are not overstressed whilst in a relatively weak state since they could be permanently deformed or subjected to damage which may not be visible.
As with concrete, it is possible to use accelerated curing schedules, either by the use of chemical accelerators or by a higher temperature cure. This may be commercially attractive, but conditions must be carefully controlled to achieve consistent and acceptable strength levels. A controlled post-curing regime is important where the conditions in storage or use will be substantially different, in either temperature or humidity, from the main cure conditions. In particular, the combination of direct sun and low humidity could cause problems with differential drying shrinkage even though the GRC strength is high at this stage in its life. GRC products will achieve a substantial proportion of their ultimate strength when the main cure is carried out for 7 days, in a humidity of greater than 95% RH, and with a minimum temperature of 15°C. A suitable post-curing regime will allow the remainder of the strength to be realized.

Air Curing

An alternative method of curing the GRC is to incorporate polymeric materials into the GRC mix. The polymer formulation used must be capable of forming a film around the mix particles, thus allowing the moisture in the GRC to be retained and hydration to continue. The polymer materials are normally added at dosage rates of between 2% and 10% of polymer solids to cement weight. After demoulding the GRC product can be allowed to cure in ambient air conditions, but care must be taken to ensure that the air temperature is above the minimum film formation temperature of the polymer. The properties of GRC cured in this way are similar to those of the same basic formulation (i.e. sand:cement ratio, water:cement ratio and glass content) made without polymer additions and moist cured as described in later. However the addition of polymer materials to GRC may affect the fire performance properties.


Saturday, 29 October 2011

Tuesday, 25 October 2011

Make your own Thermocouple sensor

If you're unfamiliar with thermocouples, OmegaEngineering's Introductionto Thermocouples is a good primer that contains several other usefulinformation resources about the selection and use of thermocouples.
One of the common tools that researchers use to measuretemperatures of objects or organisms is the electronic thermocouple. Fora few hundred dollars you can have a handheld electronic thermocouplereader and flexible thermocouple leads. The thermocouple readers arequite durable and last for years. On the other hand, the thermocouplewires eventually break after lots of usage. Most people purchasepre-made thermocouples from a source such as Omega Engineering primarily for theconvenience/cost tradeoff. However, it is fairly easy, if somewhat timeconsuming, to make and repair your own thermocouple leads using suppliesfrom Omega, which can save money in the long run compared to purchasingnew thermocouple leads every time you break one. This tutorial is basedaround the assumption that you have one of the typical Omega handheldthermometers (pictured above) and use T-type thermocouples with“miniature” connectors.


If you or your lab have standardized on some other type of thermocouple,maybe K or J type, perhaps using “standard” round-pin connectors, youcan still use the same principles described here, but the part numberswill differ.

When I aim to measure temperatures of inverts and algae, rocktemperature, or the air temperature in the field, I use T-typethermocouples with wire of a few sizes. For now we’ll considerfine-gauge wire as it is the most versatile (but least robust) form formeasuring temperatures of small things. It’s always desirable to be ableto say that the thermal mass of your measurement instrument doesn’tinfluence the temperature of the object you’re measuring (i.e. placing alarge stainless steel temperature probe at 20°C on a small snail at 40°Cmight cool the snail during the measurement process), so using smalldiameter thermocouples is good.

It can make sense financially to purchase thermocouple wire in bulk sothat you can make and repair thermocouples for years to come. Forinstance, you can purchase 40-gauge T-type insulated wire from thispage on Omega’s web site. The particular wire I would order is partnumber TT-T-40-SLE-100. This part number would get you 100 feetof 40-gauge T-type thermocouple wire with a "Neoflon" insulation. Notemy recommendation for getting the “Special Limits of Error” wire ratherthan regular wire. It costs a bit more, but Omega specs this wire to ahigher standard, so that it should be within 0.5C of the actualtemperature, rather than the 1C of the regular cheaper wire, even beforeyou calibrate.

To go with the wire, you’ll need to purchase the connectors that allowyou to plug the wire into your handheld thermometer, and in this case Irecommend connectors from thispage, using this part number combination in particular: HMPW-T-M.For starters you only need the male plugs to plug into your handheldthermometer, but you can use the female plugs to make "extension cords"by placing a female plug at one end and male plug at the other end of alength of thermocouple wire. If you have a pile of old non-functionalthermocouple leads sitting around, you can reuse the connectors.

With the wire and connectors in hand, you can now start making your ownthermocouple leads. To put things together, you’ll need the followingequipment:
Soldering iron and regular solder for electronics
Dissecting scope or magnifying glass so you can see
Razor blade or scalpel
Small screw driver, such as a jeweler’s screwdriver
Fine forceps
Some tape

Assembling the thermocouple:
Start by cutting off a length of thermocouple wire to the desiredlength. I usually make my leads a few feet long (3-4’). We’ll start byattaching the leads to the plastic connector.


Unscrew the cover on the connector. Underneath you should see two screwterminals.


On a T-type connector, one terminal will be copper colored and the otherwill be silver colored. They each have a screw in them, which is how youwill attach the thermocouple wires. Unscrew the terminal screws.Sometimes your connectors will have little Teflon washers under theterminal screws, or maybe a metal flange to help hold the wire downagainst the terminal. You can use these during reassembly, or discardthem.

Take your thermocouple wire and place one end under the dissectingscope. I like to use a bit of scotch tape to hold the wire in place sothat I can work on it with both hands. While looking through the scope,take a sharp razor blade and scrape off some of the insulation from thewire.

With the thermocouple wire I recommended above, there is a clear outerjacket, and then separate red and blue insulation around the copper andconstantan wires. Place the razor blade at a shallow angle to the wire(i.e. nearly horizontal) about 1” from the end, and scrape towards theend of the wire. Do this gently to avoid cutting through the metal wireitself. You just want to take off the clear insulation and the coloredinsulation, leaving the bare wires intact. The 1” length gives youplenty of bare wire to wrap around the terminals in the next step. Cutaway the excess insulation so that things are neat and tidy.


Once you have your wires bared, bring in the connector. Again, this isprobably best done under the scope. With your wire still taped down,position the connector so that the bared portion of the wire will sitcompletely inside the connector when closed.


Then use your forceps to wind the bare wires around their respectiveterminal screws.


The wire color matters here: the copper colored wire needs to be screwedonto the copper-colored terminal, while the silver constantan wire needsto be screwed onto the silver terminal (again, this assumes you’re usingT-type thermocouple wire). Follow this up by carefully screwing down theterminal screws. It is fairly easy to accidentally break the wire atthis step, especially if the wire catches on the terminal screw andstarts tugging as you screw down. Use your forceps to keep everything inplace. The goal here is to get the bare wire of the thermocouple lead indirect contact with the terminal, using the screw to push the wire downonto the terminal. Also note that your two bare wires should not toucheach other inside the connector housing, so keep them separate!


With the wires screwed down, it’s time to add in a strain relief beforereplacing the plastic cover on the connector. The connectors from Omegasometimes come with square brass or copper pieces that sit in adepression at the distal end of the connector housing to act as a strainrelief. Typically these pieces simply sever the fragile wire as youscrew the connector cover back on. Alternatively, the connector may comewith a round brown silicone rubber piece with a hole through its middle.This hole is too large to grip the very fine 40 ga wire, but works fineon larger diameter wire. You can make use of the silicone rubber pieceby slipping the wire underneath the rubber so that it is pressed betweenthe rubber and the plastic of the connector case. In either case, Ialways just replace the square metal pieces or round rubber piece with asimilarly sized square piece of rubber that sits in the depression.

The rubber grips the thermocouple lead without cutting it, providing ameasure of strain relief for the terminal connections inside thehousing. I cut out little pieces of neoprene rubber purchased from McMaster-Carr, such as the rubber in thisassortment: part number 9455K666 found on this page.


At this point the thermocouple is half finished. You now need tocomplete the junction at the far end of the thermocouple lead, whereyou’ll be measuring your temperature. We typically use solder to makethis connection, as it is easy and fairly durable. The pre-madeconnectors you buy from Omega use a welded junction at the sensing end,which is more durable than solder, and will not melt at hightemperatures. Soldered connections are fine for the full range ofbiologically-relevant temperatures you’ll find in the field, but youcouldn’t use a soldered joint to measure the temperature in your mufflefurnace for example, as the solder would melt.

As before, you need to bare the thermocouple wires to make theconnection. Tape your wire down to the dissecting scope platform, anduse your razor blade once again. I recommend only baring ~1/4” or so. Inspecial cases you might want a long bare wire lead, but for mostpurposes a short bare section at the sensing end is desirable from adurability standpoint.


With the two wires bared, use your forceps to twist the two leadstogether.


This provides a bit of mechanical strength to the joint, and makes thesoldering easier. For the soldering step, fire up your iron, clean thetip (wipe it on a wet sponge), and melt a bit of solder onto the tip.Again, this next step is best done under the scope. Take your solderingiron and touch it to the twisted wire pair. If you have enough solder onthe tip of the iron, the wire pair should be “submerged” in solder.


I then draw the iron tip out towards the end of the twisted wire pair,dragging the solder pool along the twisted wires. Solder doesn’t stickwell to the wire pair, so ideally the twisted joint will retain a bit ofsolder on the two wires via surface tension. Do this quickly (touch irontip to wires, draw iron tip towards end of wires) until a bit of solderremains.


It doesn’t take much to hold the wires together. Once you have somesolder on the joint, you can test the thermocouple by plugging it intoyour handheld thermometer. You should get a temperature reading, and itshould quickly approach air temperature if the tip of the thermocoupleis sitting free in the air. Assuming the thermocouple gives you areading, you can now trim off any excess bare wire from the tip that youdon’t think you’ll need, using the razor blade or wire clippers.Occasionally you’ll end up with a big blob of solder on the tip, and Ilike to cut that off to keep the tip low-profile.
You should now have a working thermocouple.


It would be prudent to calibrate your thermocouple lead. At the veryleast, dip your thermocouple tip in a stirred ice water bath to get a 0degree C reading, and go find a water bath or some other warm water of aknown temperature (a calibrated alcohol thermometer would be usefulhere) and check your thermocouple against the water temperature. Eachthermocouple lead that you make may have a slightly differentcalibration, so it’s worth checking them and writing the calibration ona piece of tape that you stick on the thermocouple lead. Most of thetime your thermocouples will all read within 0.1°C of each other, butsome may be further off.

Now that you can make your own thermocouples, you can also repair brokenthermocouples using the same methods. You might occasionally rip thewire out of the connector, or the sensing tip might get flexed too manytimes and break, or you might wind the wire too tightly and break itsomewhere within the insulation. In every case you can just cut off theoffending end of the wire and make a new, shorter thermocouple. Be sureto recalibrate it!

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