Indian Concrete Journal

Harnessing the adsorption mechanism of PCE-based SP and dispersing agent with limestone calcined clay cement-based systems to enhance workability retention M. Santhanam, J. Smrati, B. Shantanu, S. K. Divya

Adsorption of polycarboxylate ether (PCE)-based superplasticizer (SP) on the surface of calcined clay is responsible for reducing the workability retention of limestone calcined clay cement (LC3). This study aims at harnessing the time-dependent adsorption mechanism of PCEs to improve workability retention. Further, the possibility of using sodium hexametaphosphatebased dispersing agent to improve the workability retention of LC3-based concrete is also evaluated. At first, the effect of three different PCEs on the retention of LC3-based mortar and concrete is evaluated. Furthermore, the effect of change in water-to-binder (w/b) ratio and SP dosages on retention, hydration kinetics, and time-dependent adsorption mechanism (using the total organic carbon test) is studied. Despite lower w/b ratios of 0.32 and 0.38 and higher SP dosages, concrete with good workability retention and commendable compressive strength is achieved. At higher SP dosages the surface may reach saturation in terms of adsorbed molecules, leading to significant desorption of SP into the pore solution. Although initial workability is attained at lower SP dosages for a w/b ratio of 0.45, workability loss is significant within first two hours, irrespective of binder content. The addition of dispersing agent is observed to increase the workability retention without affecting the 7-days and 28-days strength significantly. It is concluded that the workability retention can be increased by blocking the active adsorption sites of the calcined clay either using higher SP dosage or by using dispersing agents

Chemical and mechanical resistance of concrete containing ferrochrome slag aggregates T. Mohanty, P. K. Acharya, S. K. Patro, P. Saha, A. M. Khan

Rapid industrialization has produced vast amounts of solid garbage, which are then disposed of in the open with detrimental effects on the ecosystem. At the same time, because of large-scale urbanization, the demand for building materials has increased unexpectedly which leads to the draining of nonrenewable resources. Many of the industrial solid waste materials though have the potential to be utilized in the construction industry, have not been used much so far because of a lack of knowledge and public education in this regard. Ferrochrome slag (FS) generated from the ferroalloy industry has the required properties that can be used as an alternative material to natural crushed rock in the concrete industry. This paper reports on the performance of concrete prepared using ferrochrome slag as coarse aggregate replacing natural coarse aggregates (NCA) of 0-100 % at an interval of 10 %. The compressive, flexural and split tensile strength of concrete improved up to 14, 42 and 35 % on the 100 % application of ferrochrome slag in place of natural coarse aggregates. The acid, sulphate and chloride resistance of concrete containing ferrochrome slag up to 100 % improved by 15, 17 and 16 % respectively when compared to normal concrete. The results of the study would encourage the concrete industry to replace natural aggregates with ferrochrome slag aggregates which may be a step towards strengthening the economy and ecology.

Study of adding silicon dioxide on some properties of concrete nanocomposite Ahmed A. Moosa, Tabarek Jameel Qasim, Zainab H. Mahdi

In this research, the effect of nano silicon dioxide on some properties of concrete was studied. The nano SiO₂ has been added to the concrete mixtures at ratios of (0.2, 0.3, 0.4, 0.5) % by weight of cement respectively. Then, the compressive strength, density and absorbency were measured at ages (7, 14 and 28) days. SEM and EDX were used to characterize the samples. The results showed that the highest compressive strength, density, and lowest water absorption were in the mixture with nano ₂ added at 0.3 % of the weight of cement. SEM examination of the samples with 0.3% nano ₂ by weight of cement showed that the microstructure is solid from the formation of C-S-H and there are no pores

Influence of ultra-fine fly ash and nanosilica on the mechanical properties of composite fiber reinforced high performance concrete V. Sairam, A. S. Sayyad, H. M. Sujay, H. S. Rao

In this research, the strength properties of Composite Fiber Reinforced High-Performance Concrete (CFRHPC) have been investigated in three steps. First, when it is added with nano silica (NS). Second, when it is added with ultra-fine fly ash (UFFA) and NS. Finally, when it is added with NS, UFFA, steel fibers (SF) and polypropylene fibers (PPF). UFFA was introduced into the concrete as a partial replacement at proportions 0 and 15 % by weight of the cement. The proportions of NS used were 0, 1.5, 3.0 and 4.5 % by weight of cement. 1.0 % SF and 0.25 % PPF (1.25 % CF) were added to the above combinations. An aggregate-to- binder (A/B) ratio of 2.0 was kept constant, and three water-to-binder (w/b) ratios, 0.275, 0.300, and 0.325, for all the mix proportions were investigated. Hardened concrete tests performed were compressive, split tensile and flexural strength at 7 and 28 days. Furthermore, the impact resistance strength and shear strength of the CFRHPC mixes were evaluated after 28 days of curing. The results obtained from this investigation have been compared with the reference mix to draw useful conclusions. A maximum gain of 47 % in compressive strength, 30 % in split tensile strength and 17 % in flexural strength were observed. The results from this study revealed that 3.0 % NS in combination with 15 % UFFA is optimal to achieve augmented mechanical strength. Additionally, SF and PPF have also contributed towards improving the tensile, flexural, shear and impact performance of CFRHPC. However, their contribution towards improving compressive strength was found only marginal.

Experimental studies on quaternary blended concrete under acid resistance, sulphate resistance, water permeability, and chloride permeability V. Kiran Kumar, , T. S. Seshadriand, P. S. Rao

Use of mineral admixtures in high strength/high performance concrete is gaining importance due improved performance in durability performance and mechanical properties in addition reduced cement content which in turn reduces the carbon emissions. The use of nano materials is becoming more popular which enhances concrete properties through increased reactivity and pore filling due to its fineness. Durability performance is an important parameter to consider when designing concrete, and it can be accomplished through the use of mineral admixtures. Many studies have been conducted in the past using mineral admixtures such as Fly ash, metakaolin, micro silica, and nano silica in binary, ternary, and quaternary blends and discovered that enhanced performance regarding strength and durability. This experimental study looks at the impact of Metakaolin, Fly ash, and Nano silica in quaternary blends and the durability properties such as Acid resistance with 5 % HCl and H₂SO₄, Acid durability factor, Sulphate attack exposed to 5 % MgSO₄, Water permeability, and Rapid chloride permeability test are made at 28, 90 and 180 days. The findings shows that, due to the use of mineral admixtures quaternary blended concrete has shown improved performance than control concrete because of the improved pore refinement and dense structure.