17-12-2012, 01:58 PM
Effect of Sulphate Attack on Self compacting Concrete
ABSTRACT
To achieve SCC properties, the concrete mix should contain lower volume of coarse aggregate(1). SCC requires higher powder content, lesser quantity of coarse aggregate, high range Superplasticizer and VMA to provide Stability and fluidity to the concrete mixes. The flow characteristic increases with increasing VMA. Compressive strength, flexural strength and Split tensile strength decreases with increased addition of VMA
Substitution of 10% of cement with Quarry limestone powder (QLP) improved the compressive strength of cement pastes(2), which can be accepted as a positive factor in utilization of QLP in Self–compacting paste applications. QLP can successfully be used in production stage of proper SCC mixtures. Incorporation of QLP at the same cement content generally reduced the superplasticizer requirement and improved the 28 days compressive strength of SCCs. Normal strength SCC (~30 Mpa) mix that contain approximately 300-310 kg of cement per metre cube can be successfully prepared by employing high amount of QLP. However, substitution of high amount of cement with QLP reduced the strength values.
The SCC has become widely used standard concrete rather than a special concrete(11). The new structural design and construction systems are making full use of SCC in durable and reliable concrete structures. Different testing methods to test high-flowability, resistance against segregation, and passability(6). It is difficult to develop SCC with CA content higher than 45% or lower than 15% of the total aggregate(5). SCC properties can be achieved even for a very high percentage of sand content (up to 85%). Strength and workability properties of SCC containing different combinations of admixtures improved as a dosage of superplasticizer in them increased(4). No adverse effects observed in the combination of admixtures, mainly because of using the admixtures from the same manufacturer.
Optimum water/cement ratio for producing SCC is in the range of 0.84–1.07 by volume(8). The ratios above and below this range may cause blocking or segregation of the mixture, respectively. Self-compactability test method stipulations are not universally accepted rules. Degree of toleration depends on the engineering judgment, material type and variety. Proper concrete mixtures can be produced by trial and error method. Limestone was the most common addition in most of the cases. Approximately half the cases used a viscosity-modifying agent (VMA) in addition to superplasticizer and could therefore be considered as a combined type of SCC, which are generally more robust than mixes without a VMA(7). It was found that the quarry dust could be used successfully in the production of SCC(12). However, due to its shape and particle size distribution, mixes with quarry dust required a higher dosage of superplasticizer to achieve the flow properties.