Table 1. Compressive strength test results when subjected to sulphate attack
This paper presents an experimental investigation on the effect of acid attack on the properties of SCC produced by the combination of admixtures such as (Superplasticizer + Viscosity modifying admixture + Air entraining agent + Accelerator), (Superplasticizer + Viscosity modifying admixture + Air entraining agent + Retarder), (Superplasticizer + Viscosity modifying admixture + Air entraining agent + Water proofing compound) and (Superlasticizer + Viscosity modifying admixture + Air entraining agent + Shrinkage reducing admixture). The concrete testing specimens was prepared by a mix proportion 1:2.7:6.1:5.1 with cement: fly ash: sand: coarse aggregate with a water/binder ratio of 0.38. Specimens after 28 days of curing were immersed in sodium sulphate solution of 5% and 10% concentrations for 90 days. After 90 days of immersion, the specimens were removed from sulphate media, weighed accurately and tested for their respective strengths. SCC produced with above combination of admixtures show better resistance to sulphate attack as compared to SCC produced with combination of admixtures (SP+VMA) only.
The concrete technology has made tremendous strides in the past decade. The development of new technology in the material science is progressing rapidly. In recent two or three decades, lot of research was carried out throughout the globe on improving the performance of concrete in terms of strength and durability qualities. Today we can prepare any type of concrete to suit the site conditions. Now the concrete is no longer a material consisting of cement, sand, aggregates and admixtures, but it is an engineered material with several constituents. To obtain good concrete all good practice of operations of concrete have to be taken care. Meticulous care has to be exercised during proportioning, mixing, placing, compacting and curing. Negligence in any one operation may damage the concrete severely. One of the most important operations of concrete is consolidation or compaction. But is very difficult to achieve 100% compaction economically. Thus it was the dream of concrete technologists to invent a concrete, which does not need compaction and fills every cavity by its flow characteristics. This dream of concrete technologists came true when Okamara invented self compacting concrete in 1988 in Japan. The studies on self compacting concrete were further reinforced by Ozawa and Meekawa of Japan. Self compacting concrete is a mix that can be compacted into every corner of formwork, by means of its own weight and without the need for vibrating compaction. Inspite of its high flowability, the coarse aggregate is not segregated. The alternate wetting and drying affects the durability of concrete. There is an in built assurance of uniform placement and fully consolidation concrete when self compacting concrete is used at site this ensures high durability since air voids and other flaws are likely to be absent in self compacting concrete. The development and uses of self compacting concrete has increased in these years. Given its highly flowable nature self compacting concrete can flow readily under its own weight, fills restricted sections and congested formwork without segregation. EFNARC has published specifications and guidelines for self compacting concrete (EFNARC 2002).
The main objective of this experimentation is to study the effect of aggressive environments on the properties of SCC produced by the combination of admixtures such as (Superplasticizer + Viscosity modifying admixture + Air entraining agent + Accelerator), (Superplasticizer + Viscosity modifying admixture + Air entraining agent + Retarder), (Superplasticizer + Viscosity modifying admixture + Air entraining agent + Water proofing compound ) and (Superlasticizer + Viscosity modifying admixture + Air entraining agent + Shrinkage reducing admixture). The aggressive environment considered in the study was sulphate attack of different concentrations.
Cement: 43 grade ordinary Portland cement (OPC) with specific gravity of 3.15, complying with IS: 8112-1989.
Fine aggregate: Locally available sand with specific gravity of 2.63 falling under zone II, complying with IS: 383-1970.
Coarse aggregate: Locally available coarse aggregate with specific gravity of 2.88 complying with IS: 383-1970.
Flyash: Obtained from Thermal Power Station, Shaktinagar, Raichur.
Viscosity modifying admixture: A viscosity modifying admixture called Structuro 485 was used to induce the flow without segregation. It was used at the rate of 0.30% weight of binder (cement + flyash)
Superplasticizer: A high performance concrete superplasticizer Structuro 100 based on modified polycarboxylic ether was used. It was used at the rate of 0.40% by weight of binder (cement + flyash).
Air entraining admixture: Air-entraining admixture used in the experimentation was Conplast PA21(S). It was used at the rate of 0.30 % by weight of cement.
Retarder: The retarder used in the experimentation was Conplast RP264.It was used at the rate of 0.4% (by weight of cement).
Accelerator: The accelerator used in the experimentation was Conplast NC. It was used at the rate of 2% by weight of cement.
Water proofing compound: The water proofing compound used in the experimentation was Conplast X421 IC. It was used of at the rate of 0.30% by weight of cement.
Shrinkage reducing admixture: The shrinkage reducing admixture used in the experimentation was Cebex 100. It was used of at the rate of 0.45% by weight of cement.
The concrete was prepared by a mix proportion 1:2.7:6.1:5.1 with cement: fly ash: sand: coarse aggregate with a water/binder ratio of 0.38. Now the admixtures taken in order were added in the required quantities and thoroughly mixed. At this stage concrete was in a flowable state. Concrete mix was poured in the moulds to prepare the specimens for strength tests.
For sulphate attack test, the specimens after 28 days of curing were immersed in sodium sulphate solution of 5% and 10% concentrations for 90 days. Before immersion, they were weighed accurately. After 90 days of immersion, the specimens were removed from sulphate media, washed in running water, weighed accurately and tested for their respective strengths.
Compressive strength specimens were of dimensions 150 x 150 x 150mm and were tested as per IS 516:1959. Tensile strength specimens were of 150mm diameter and 300mm length. Split tensile strength was conducted on these specimens as per IS 5816:1999. Flexural strength test specimens were of dimensions 100mm x 100mm x 500mm. Two point loading was adopted on an effective span of 400mm while conducting the flexural strength test as per IS 516:1959. Impact strength test was conducted on specimens of dimension 150mm diameter and 60mm height. Schruders impact testing machine was used for this purpose.
The following tables give the details of the experimental results of self compacting concrete subjected to sulphate attack.
The following Table 1 gives the compressive strength test results of SCC with different combination of admixtures subjected to sulphate attack.
The following Table 2 gives the tensile strength test results of SCC with different combination of admixtures subjected to sulphate attack.
The following Table 3 gives the flexural strength test results of SCC with different combination of admixtures subjected to sulphate attack
The following Table 4 gives the impact strength test results of SCC with different combination of admixtures subjected to sulphate attack
Table 1. Compressive strength test results when subjected to sulphate attack
Table 2. Tensile strength test results when subjected to sulphate attack
Table 3. Flexural strength test results of SCC when subjected to sulphate attack
Table 4. Impact strength test results of SCC when subjected to sulphate attack
The authors would like to thank the Principal of KLESCET Belgaum and the management authorities for giving encouragement for the research and S.J.M. Institute of Technology, Chitradurga, for their constant encouragement. The authors also indebted to Vice-Chancellor, Christ University, Fr. Benny Thomas, Director and Dr. Iven Jose, Associate Dean, Christ University Faculty of Engineering, Bangalore for their encouragement.