دانلود رایگان مقاله انگلیسی مقاومت و دوام بتن حاوی ترکیبات بتنی بازیافت شده - الزویر 2018

Abstract

Crushed concrete aggregates sourced from waste concrete are a sustainable alternative to natural crushed stone aggregates. This paper presents a study to evaluate the potential of replacing natural crushed stone aggregates in concrete with crushed concrete aggregates (CCA). Mathematical models were developed using regression analysis to account for the effect of aggregate replacement on the strength parameters of concrete. The strength and durability properties of concrete containing CCA were evaluated by a comprehensive experimental investigation involving nine control mixes. The variables considered in the experimental study are water cement ratio, cement content in concrete and percentage replacement of coarse aggregate (CA). The strength properties such as compressive strength, modulus of elasticity, split tensile strength and flexural strength are studied. The results obtained from the present study and data available in published literature were used for the development of the strength prediction models. Durability properties such as water absorption, sorptivity, acid attack resistance and chloride permeability are determined in this study. The test results showed that up to 25% of natural crushed stone aggregates in concrete may be replaced with CCA without significantly affecting the strength of concrete and that the partial replacement of natural aggregates with CCA can be recommended in areas of moderate exposure conditions. The mathematical models developed in this study can be used for the a priori prediction of the strength parameters satisfactorily. These models serve as simple tools to estimate the strength of concrete with different levels of aggregate replacement using CCA and can be used as design data of CCA concrete in structural members. A mix design methodology has been proposed using the models developed to aid the practicing engineers to arrive at the mix proportions of CCA concrete.

7. Conclusions

From the present study, the following conclusions have been arrived at:

· The replacement ratio of aggregates has a significant effect on the strength properties of concrete. Replacement of natural aggregates with up to 25% CCA does not alter the strength properties of concrete remarkably. Beyond 25% aggregate replacement, the compressive strength and modulus of elasticity of CCA concrete are affected.

· The reduction in the splitting tensile strength and the flexural strength of CCA concrete with increase in the percentage of CCA is comparatively lesser than the reduction in compressive strength and modulus of elasticity.

· Durability of CCA concrete decreases with increase in the percentage of CCA in the mix. Higher water absorption by CCA and the presence of porous mortar adhered to the surface affects the durability of concrete.

· Durability of CCA concrete improves with the increase in the cement content of the mix and may be due to the improvement in the quality of the hydrated cement paste and its density.

· CCA concrete with 25% replacement of natural aggregates can be recommended in areas with exposure conditions deemed to be ‘Moderate’ as per ASTM C1202 [21].

· The models developed in the study are able to predict the strength properties of CCA concrete quite accurately for a wide range of input data.