Test for Performance Evaluation of Construction Chemicals in Concrete Structures

Test for Performance Evaluation of Construction Chemicals in Concrete Structures

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The usage of construction chemicals is becoming inevitable in the modern construction. Inspite of the fact that these materials are in use for the past couple of decades in the country, the users have to often just accept the claims of the manufacturers in regard to the properties and performance of these materials. This is either due to lack of knowledge or adequate facilities for testing or both. In many of the Indian cases Indian Standards are also not available.

An attempt is made in this paper to compile the various codal specifications and procedures to conduct performance tests on most commonly used construction chemicals. This paper does not provide a comprehensive account of all the tests for construction chemicals but only highlights the minimum tests necessary for performance evaluation.

 

M N Ramesh
Director
Talrak Construction Chemicals Pvt. Ltd.
Bangalore

 

Introduction

The most commonly used construction chemicals in the country are

– Chemical Admixtures for concrete
– Curing Compound
– Bonding Agents
– Free flow non Shrink grouts
– Special mortars for repair and Protective coating

Chemicals which are added to the concrete at a low dosage (<5% by weight of cement) at the time of mixing to modify the properties of concrete both in plastic and hardened state are known as chemical admixtures. Plasticizers, superplasticizers and Integral waterproofing compounds fall in these categories of materials.

Chemicals that are applied on semi hardened or hardened concrete essentially to enhance the performance characteristics form another category. Eg. Curing compound, bonding agents, protective coatings etc.,

Chemicals (formulated Prepacked ready to use materials) which are used directly to compensate the inherent deficiencies of normal concrete or to reinstate or streng-then the distressed concrete form the category to which grouts, special mortars for repair etc, belong.

Functions and Evaluation Parameters

Plasticizers / Superplasticizers and Integral Waterproofing compound

The widely used materials among concrete admixtures are plasticizers, super-plasticizers and Integral waterproofing compounds. They are mainly used for reducing water content in the concrete mix, improve the workability of concrete in the plastic state and to enhance strength and durability of concrete in the hardened state. In case of Integral Waterproofing compounds, it is used to enhance the water impermeability of hardened concrete.

The performance tests to evaluate the efficiency of these materials are aimed at measuring these parameters of admixed concrete and comparing them with those of controlled mix or reference mix.

Curing Compounds

The objective of application of a curing compound at the early stage of concrete setting is to rentain internal moisture to aid hydration process in concrete without the need for water curing. The main parameter to be tested for evaluation is the water loss in concrete applied with curing compound.

Bonding Agents

The usage of bonding agents is essentially to achieve monolithicity between hardened and plastic concrete segments especially when an old construction is continued. The monolithicity of the member often depends on the efficiency of the joint at the interface. The bonding agents performance is evaluated by testing the bond strength and mode of failure, when the test specimen is subjected to specific load. Generally the bond strength shall be more than the tensile strength of concrete and the failure should be away from the joint interface for an efficient bond.

Protective Coatings

Special coatings are applied on hardened concrete surfaces to protect the concrete and reinforcing steel or pre-stressed cables from chemicals and /or environmental attack. These coatings should possess special barrier properties, mechanical properties such as adhesive strength, breathability and resistance to host of exposure conditions such as UV rays. The performance evaluation of protective coatings is done by measuring these parameters and comparing the results with the values specified in codes.

Non Shrink Grouts and Special Mortars

The normal concrete suffers with some inherent deficiencies. The important ones being limited workability at a high target strength and shrinkage. Due to this normal concrete alone cannot be used to effectively transfer loads from machines for example, on the foundation, owing to in-adequate contact with the base plate due to shrinkage of concrete. This is generally overcome by using non-shrink, free flow, high strength cementitious / epoxy grout.

The performance evaluations of these grouts are tested by measuring the critical parameters such as shrinkage compensation, flowability and strength.

The specially formulated mortar such as polymer modified mortars epoxy mortars microconcretes for reinstatement / strengthening of concrete structures in distress should possess special properties such as good bond strength, impermea-bility to water and gases, dimensional stability and other mechanical properties. The performance assessment is done by subjecting these materials to various tests for the estimation of the above properties.

Performance Tests

Plasticizers and superplasticizers

The tests for evaluating the performance of plasticizers and superplasticizers are conducted directly on the concrete mix with the admixtures.

First a reference concrete mix is done. Then the parameters of admixed concrete are compared with those of the control mix, and the result are expressed as follows :

– Water content as percentage of control sample.
– Initial and Final setting time as deviation from control sample
– 3,7,28 days, 6 months and 1 year compressive strength as percentage of control sample
– Flexural strength as percentage of control sample at 3, 7 and 28
– Length change as percentage increase over control sample

Bleeding and percentage increase over control sample

The stipulations table provided for each of the above parameters as laid down in IS : 9103 – 1979 are reproduced in table 1.

 

 

Water content tests (IS : 1199-1959, IS:9103-1079 and IS:2386 (Part – III)- 1963)

The net water content in the concrete mix is calculated taking into account the absor-ption water in the aggregates (Wn). The concrete mix shall then be compacted into a unit weight container and compacted density of concrete is calculated (W). The volume of concrete shall be calculated by dividing the sum f the weights of the ce-ment, aggregates, and water in the batch of concrete by unit weight of concrete (V) expressed in m3. The mass of cement per m3 shall then be calculated by diving weight
of cement by volume of concrete/batch in m3 = C.

Water cement ratio shall be determined using Wn / C. The relative water content for the concrete containing admixture shall be expressed as a percentage of the water content of the control mix.

Setting Time of Concrete by penetration resistance

Preparation of specimen : The mortar is separated from the concrete sample by sieving with 4.75mm IS sieve. The mortar is remixed and compacted in a container in layers by tamping rod and levelled and kept in shade. Bleeding water if any shall be removed from surface with the help if pipetted or sponge.

Apparatus: Penetration resistance appa-ratus with removable nedles of size 645,323,161,65,32,16 mm2 bearing area.

Procedure : The appropriate size of needle is fitted to the penetration resistance apparatus. The needle is pressed against the mortar surface until it penetrates to a mark of 25 mm. The force required to a penetration of 25mm is recorded on the equipment. The penetration resistance is calculated by dividing the force by the bearing area of the needle used. The process is repeated at every one hour and a plot of penetration resistance versus time is obtained.

Setting Times: The time of initial and final setting is obtained from the plotted curves at which penetration resistance of 343 N/mm2 and 26.97N/mm2 respectively are reached. The results are expressed as division from the control sample.

Compressive strength

The concrete cubes of 150mm sides are casted as per IS 516 – 1959 using both control mix and admixed concrete. Then cubes shall be cured as per standard practice and tested for compression at 3,7,28 days, 6 months, 1 year. The results of the compressive strength of concrete with admixed concrete are expressed as a percentage of that of control concrete.

Flexural Strength

The flexural strength test prisms of size 100 X 100 X 500mm shall be cast using appropriate mould with control mix and admixed concrete. This specimen shall be cured and tested for flexural strength at 3,7 and 28days as per IS:516-1959. The results of admixed concrete is expressed as a percentage of that of control mix.

Length Change:

The typical apparatus used for this test is shown in Fig.1. The test prism of size 75 X 75 X 150mm are cast in appropriate mould using both control mix and admixed concrete. Two steel balls of 6.5mm dia are embedded on either faces of prism at the centre. This specimen shall be kept moist for 24hrs followed by water immersion curing for 28 days. After the completion of curing the specimens are removed and wiped dry. The specimen shall then be dried in an oven at a temperature of 50± 10C for 44hrs, and taken as above at a control temperature of 270C. The cycle of dry cooling and measuring is repeated till a constant length is attained.

 

 

The final reading is taken as the dry measurement. The length of the specimen shall be measured adjacent to the nearest 0.5mm and this is taken as a dry length. The length change is calculated as the difference between original wet measurement and dry measurement. The result of admixed concrete is expressed as percentage increase over control sample.

Bleeding

The fresh mixed concrete is compacted in layers of 50mm in a cylindrical container to a height of 250mm and finished with a trowel. Noting the time, container is kept on a levelled surface at a controlled temperature of 27± 20C coving with a lid and a weight of sample is taken (S). The water accumulated if any on the top surface is pipetted out at every 10 minutes intervals during the first 40minutes and at 30minutes interval subsequently till the bleeding stops. The collected water shall be transferred to a measuring jar and the volume is noted.

Bleeding water percentage is calcu-lated = VW X 100 /W/w X S

Where,

VW = Volume of bleeding water in ltrs
W = The net weight of water in batch in kg
w= Total mass of the batch in kg
S = Weight of sample in kg

The bleeding percent increase of admixed concrete over the control mix is computed.

 

 

Integral Waterproofing Compounds

The efficiency of the integral waterproofing compounds is estimated by conducting permeability test on mortar specimens. The method of test is covered in IS:2645-1975. However, IS:3085-1965 also provides permeability tests methods both for mortars and concrete which is used for general purpose.

Principle of Test

This method of test aims at determining the permeability to water through cement-sand mortar specimens prepared with and without the integral waterproofing compound and cured under specified conditions.

Test Method

Preparation of test specimen : A cylindrical test specimen is cast using a cement-sand mortar in a cylindrical mould and cured for 28 days under water and controlled conditions of temperature and humidity. After curing the specimen shall be sub-jected to water percolation in a permeability test unit. The general arrangement of which is shown in Fig.3

 

 

Acceptance Criteria: If the average percolation (measured in ml of water) for specimen with waterproofing compound is less than 50% of the average percolation of the control specimens, the integral waterproofer under test is considered satisfactory.

Curing Compound

The curing compound under evaluation is applied as a uniform coating usually by spraying to the levelled surface of freshly mixed mortar in a metal mould. The mortar is of proper 1:3 by weight with w/c = 0.44 using a standard cement and sand. The control specimen and uncoated control specimens are then cured for 72± 15mins in a cabinet in which dry air is circulated. The specimens are weighed after completion of curing. The efficiency of curing compound is calculated from the measured loss in mass of the specimen after correction from the loss of solvent from the coated specimens. The results will be the curing efficiency index E expressed as a percentage of difference in water loss of control coated sample to the loss of water of the control sample.

Where,

E = Efficiency index
Wc = Loss of water from the control specimen
Wt = Loss of water from the test specimen coated with curing compound

The test methods are covered under BS:7542-1992. However in ASTM C156-80A the results are expressed as water loss over a specific unit area. Then acceptance criteria as per ASTM C309-89 is given as a water loss of 0.55kg /m2 of area in72hrs.

Bonding Agents

The performance of bonding agents is tested by slant shear bond strength. The test method is covered in BS:6319-Part IV and ASTM C882-87. Principle of this test is conducting compression test on a com-posite specimen formed by joining two segments of the prism (as per BS:6319) or cylinder (as per ASTM C – 882) scarf jointed at 300C to its main axis using the bonding agent under test. The result is simply ex-pressed as the compressive strength of the composite specimen and the observation is made on the mode of failure.

The bond strength is calculated by dividing the load at failure by the area of the bonded surface.

Generally the bonded agent is accepted if the failure is a compression failure away from the bond line.

Free Flow Non-Shrink Grouts

The performance tested for evaluating the efficiency of a grout are conducted in respect of the following parameters

a) Shrinakge compensation or free expan-sion
b) Flowability and
c) Compressive strength at 1,3,7 and 28
days.

Plastic Expansion

The procedure of conducting expan-sion test is covered in FIP (Federation Inter-nationale Dele Pre Contrainte) specification FIP.2.1 Sept.75.

The grout immediately after mixing with water as per manufacturer specification is poured into a 100mm side cube mould to about 80% of its depth. The expansion takes place only at the unrestrained top sur-face of the grout which can be measured by estimating extent of lifting of a light weight plastic disk placed on the free surface of the grout. The readings are measured using a pointer fixed to the disc which intern moves over a graduated scale fitted on a mirror to avoid parallax error. The expan-sion is expressed as a percentage of the original level.

Acceptance Criteria

ASTM C-117-91A specifies a plastic expansion of a minimum of 0% and a maximum of 4%

ii) Hardened Expansion

The hardened shrinkage compensation tests are conducted in line with the shrinkage test explained for concrete, mortars.

The acceptance criteria for hardened expansion is a minimum of 0% and a maximum of 0.3% at 1,3,14 and 28 days as per ASTM C 1107-91A.

As per CDR-C 621-89 (Corps of Engineers specification for nonshrink grout) the hardened expansion of grout shall not be greater than 0.4% and not less than 0% at 3,14 and 28 days.

iii) Flowability

The fluidity of the grout is determined by the following methods

a) B.S Cone method
b) CRDC Cone method
c) Marsh Cone test
a) B.S Cone Method – In the B.S Cone method, the mixed grout under test is filled in a truncated brass cone having the top internal diameter of 38±0.5mm and bottom internal diameter of 66+0.5mm and a height of 90±0.5mm. Conforming to BS:6463 the cone is lifted allowing the grout to spread on the flow table. Flowability is measured as a diameter of spread of the grout. The acceptance spread depends upon the nature of application as specified by the user. The typical cone is shown in Fig.4.
b) CRD-C /Marsh Cone method – In this method the time taken by a specific volume of grout to flow out of a standard cone as shown in Fig.5 known as efflux time. The volume and the dimensions of CRDC and Marsh Cons is presented in Table 2.

 

 

Acceptance criteria as per CRDC for cementitious grout are 10 to 30 secs of efflux time using CRDC cone for fluid grouts.

Compressive Strength

The method of test for compressive strength is specified by IS:4031(part VI)1988, ASTM C109 and BS:4551-1980, DIN 1164 for cementitious grouts and BS::6319(Part II) for epoxy grouts.

The various sizes of the tests speci-men as per different standard is given in Table – 3

 

 

Special Mortars for repair

The important tests for the performance evaluation of special mortars are:

a) Bond strength of mortar to substrate using LIMPET tester
b) Water permeability test
c) Dimensional Stability Mechanical Pro-perties

Limpet Test

This test is aimed at assessing in-situ bonding of the repair mortar to the substrate by measuring the tensile force required to pull off the mortar from substrate. Ge-neral schematic sketch showing principle of test is as per Fig.6.

 

 

Test Method

The area on the repair mortar to be tested is selected and using the core cutter supplied with the equipment, cores are cut to a depth of 5-10mm into the substrate. The surface of the core is cleaned, and dolly is fixed using an epoxy adhesive and allowed for curing. The limpet equipment is placed on the top of the dolly and the pull rod is fixed in place. The turing knob is turned until the failure takes place. The pull out force at failure is recorded from the equipment.

Acceptance Criteria

The mode of failure should not occur in the mortar or in the joint.

Water Permeability Test

The water permeability test is carried out as per IS:3085-1965.

Test Method

The test specimen is cast using the repair mortar in a split mould of required size. The specimen shall be cured for 2 days or as per manufacturer’s specifications. The specimen shall be demould and placed in the permeability cell (as shown in the fig).

A standard pressure of 10kg/cm2 is applied to the specimen unless stated by the manufactures otherwise, until a steady state of flow is reached. The test is done for 100hrs.

The correction factor for evaporation losses and the caliberation of equipment should be done as per the equipment manual

Calculation:

Where,
K = Co-efficient of permeability in cm/sec
Q = Quantity of water in ml percolating over the entire period of test, after reaching the stead state A = Area of specimen face in cm2
T = Time in second over which Q is measured
H/L = Ratio of pressure head to thickness of specimen both in same units.
Dimensional Stability

The repair mortar is evaluated in res-pect of dimensional stability conducting shrinkage tests both in plastic and harde-ned state.

Plastic Shrinkage

This test is similar to the one explained for grouts under plastic expansion.

Hardened Shrinkage

The repair mortar under test is cast in an annular ring of outer diameter 175mm and inner diameter of 104mm and the height of 64mm. The outer ring removed after 24hrs and the specimen is air cured for the specified period. Observations are made for development of either radial or diametrical cracks on the ring.

Acceptance Criteria

The mortar is accepted if the specimen does not exhibit any crack over 28 days.

Mechanical Properties

The mortar under evaluation is tested for mechanical properties such as com-pressive strength, flexural strength and direct tensile strength, IS:4031, BS:4551-1980 is refered for these tests.

Protective Coatings

The nature of performance evaluation tests for protective coatings depends on the type of coatings used.

Chemical Resistance Test

For chemical resistance coatings for concrete, the coated concrete/mortar sample using the coating material under test is immersed into the chemical of specified concentration whose effect on the coating is to be studied. Generally, immersion, spraying, drying and wetting cycles and temperature seasoning test with chemicals are carried out. The period of exposure is yet another parameter to be considered for chemical resistance test.

Klofer Test for water vapour transmission

Breathability is a term used for the ability of the coating for water vapour transmission without allowing water to pass through it. This test is known as Klofer test for water vapour transmission. It consists of a water bath and a humidity control chamber separated by the coated membrane. Due to differential water vapour pressure the water from the bath evaporates through the coating towards the control humidity chamber in an attempt to achieve an equilibrium. The weight loss in the bath is measured daily to obtain a study state of flux. The flux can be converted into meters of still air barrier.

Klopfler test for Carbon dioxide diffusion :

This test also has the same regime as above. Instead of water bath sodium hydroxide pellets which are highly hyroscopic are kept in a container in a CO2 + air mixture chamber, separated by a coating membrane. The weight gained by the sodium hydroxide pellets is taken daily which gives the rate of carbon dioxide diffusion through the coating.

Chloride ion diffusion co-efficient test.

This test also has the same regime as above. Instead of water bath sodium hydroxide pellets which are highly hyroscopic are kept in a container in a CO2 + air mixture chamber, separated by a coating membrane. The weight gained by the sodium hydroxide pellets is taken daily which gives the rate of carbon dioxide diffusion through the coating.

Chloride ion diffusion co-efficient test.

A concrete slice is applied with the coa-ting under test and conditioned at 60±5% RH an 23±10C for a period of 28 days.

The coated specimen and uncoated specimen (controlled) are placed in indivi-dual mould and the edges are sealed with epoxy resin and cured.

The coated specimen is mounted on a diffusion cell as shown in Fig.8. The CI¯ diffusion through the coated sample is determined at suitable intervals using CI¯ selective electrodes connected to a digital volt meter. A standard solution of sodium chloride in saturated lime water is used to construct a calibration curve. The diffusion co-efficient through the coated sample is compared with that of controlled sample.

 

 

Conclusion

The methods of test and acceptance criteria discussed in this paper serve as a general guidelines for the user of construction chemicals to evaluate the material under consideration. However, there are other tests also available for evaluation. The acceptance criteria may vary depending on the application and site conditions.

For further details:
Talrak Construction Chemicals Pvt. Ltd.
#148 (First Floor), Sri Gururaghavendra Complex Basaveshwara Circle,
BEML 3rd Stage Rajarajeshwari Nagar, Bangalore – 560 098.
Phone: +91-9663101013
Email: chethana.g@talrak.co.in
Web: www.talrak.co.in

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