Durability studies of concrete

Durability studies of concrete

One major challenge facing the civil engineering community is to execute projects in harmony with nature using the concept of sustainable development involving the use of high performance, environment friendly materials produced at reasonable cost. In the context of concrete, which is the predominant building material, it is necessary to identify less expensive substitutes. According to Prakash Rao , replacement of natural sand to the artificial sand with dust, artificial sand can be used for making good concrete.It helps in conservation of natural sand. Mahendra found that the sharp edges of the particles in artificial sand provide better bond with the cement than the rounded part of the natural sand.

According to Mehta , the three fundamental elements for supporting an environment friendly concrete technology for sustainable development are the conservation of primary materials, the enhancement of the durability of concrete structures, and a holistic approach to the technology. Regarding the conservation of primary materials, reductions in the consumption of cement, aggregates and water, along with the use of waste materials and industrial by-products, are the principal actions to be taken in order to reduce the utilization of non-renewable resources and the negative impact on the environment. The main objective of the present investigation was to study the strength and durability performance of concretes made with natural sand and artificial sand with dust. The durability properties were investigated through micro-structure related properties of concrete, such as, permeability, water absorption, chloride diffusion, and also through chemical attack.

Materials

Ordinary Portland cement (Murli) conforming to the requirements of IS:1489 (43 grade) was used. Crushed granite with grain size of 12 mm and 20 mm for normally vibrated concrete and a good quality well graded river sand, and artificial sand with dust were used as coarse and fine aggregates, respectively.

Mixing, demoulding and curing

Thorough mixing and adequate curing are most essential for achieving a good concrete. In the laboratory, the concrete was mixed in a pan mixer of 100 litre capacity. The mixing time was kept to about 3–4 min for normal concrete. Generally, the demoulding was done 24 hr of casting. Potable water was used for curing all the concretes. All the concretes were kept in moist environment immediately after the initial set and before the demoulding.

Properties of fresh concrete

In the present study, the slump flow are used for noting the slump and passing ability of the concrete.

TEST PROGRAM

Compressive strength studies

The compressive loading tests on concrete were carried out on a compression testing machine of capacity 2000 kN. For the compressive strength test, a loading rate of 2.5 kN/s was applied as per IS: 516–1959. The specimen used was 100 mm cube. The test was performed at 28, 90 and 180 days. The specimens were tested immediately after taking the cubes from curing tank in surface dry condition.

Permeable voids and water absorption studies

Usually water permeability characteristics are used for assessing durability characteristics. Permeability can be measured by conducting water permeability test as per standards, percentage of water absorption test and initial surface absorption test. In the present investigation, percentage of water absorption and percentage of permeable voids were determined as per the procedure given in ASTM 642–82 . The absorption and permeable voids were determined on two 100 mm cubes. Saturated surface dry cubes were kept in a hot air oven at

105°C till a constant weight was attained. The ratio of the difference between the mass of saturated surface dry specimen and the mass of the oven dried specimen at 105°C to the volume of the specimen (1000 milli litre) gives the permeable voids in percentage. The oven dried cubes after attaining constant weight, were then immersed in water and the weight gain was measured at regular intervals until a constant weight was reached. The absorption at 30 min (initial surface absorption) and final absorption was determined. The final absorption in all cases was determined at 96 hrs. According to Dinakar , the absorption characteristics indirectly represent the volume of pores and their connectivity.

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