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Theses

Assessment of fresh and hardened properties of concrete made of crushed aggregates containing no natural sand

Abstract : In Lebanon, good quality natural siliceous sand becomes rarely available, and for environmental reasons, its extraction is subjected to governmental restrictions. This problem affects the construction sector through the cost and the quality of concrete. Moreover, this sand is too fine to be used alone as fine aggregate in concrete mixes. Therefore, to meet the grading requirement of the ASTM C33, the standard applied in Lebanon, this sand is currently mixed with an appropriate proportion of a coarser crushed limestone sand which compensates the fineness of the natural sand. Accordingly, finding an alternative to natural sand in concrete becomes essential to reduce its economic and environmental problems and to avoid the dependency of the construction field on its quality and availability in the Lebanese market. After a literature review of existing alternatives around the world, it seems that the replacement of natural sand by the local crushed limestone sand could be an appropriate solution in the Lebanese context due to the abundance and good quality of this sand. Hence, the current study is the first in this country that aims to give scientific evidence of this solution before being applied in the Lebanese market. Its objective is to assess the effect on the concrete performance of the total replacement of natural siliceous sand by crushed limestone sand. In order to respond to the objective of the study, the behaviors of concrete mixes incorporating normalized crushed sands without natural sand are compared to those of reference concrete containing the conventional combination of natural sand and crushed sand, to verify that their performances could be maintained, for three normal strength concrete mixes and one high strength concrete. Since the crushed sand, provided currently from the limestone quarries, is too coarse to directly replace the natural sand, the first step consists of constructing two types of normalized crushed sand conforming to the standard grading requirements. For each type of fine aggregate, the fresh concrete properties, mechanical behavior, and durability are investigated. The effects of the mineralogy, morphology, and particle size distribution of fine aggregates on these various properties are then evaluated. A microstructural analysis is also conducted to depict the variations at the interface between the cement paste and the different types of sand grains and to try to explain the differences that could exist at the macro scale between the different types of concrete. Furthermore, since the production of the normalized crushed limestone sand could impose many industrial and economic constraints to limit the high percentage of fines, the performance of normal and high strength concretes, incorporating crushed sand with a percentage of fines (< 75 µm sieve) exceeding the limit imposed by ASTM C33 (7%), is evaluated following a performance-based approach. For fixed water to cement ratio, cement content, and coarse aggregates proportions, and for different dosages of admixture to reach the same slump value, the results prove that the concrete performance could be maintained when using the normalized crushed limestone sand conforming to the standard grading requirements or the fine crushed limestone sand with a high percentage of fines. Additionally, the overview on the economic and environmental impacts on the Lebanese context verifies the feasibility of the use of crushed limestone sand as the only fine aggregate.
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Submitted on : Monday, September 13, 2021 - 5:34:10 PM
Last modification on : Monday, April 4, 2022 - 3:24:17 PM

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  • HAL Id : tel-03343018, version 1

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Faten Abi Farraj. Assessment of fresh and hardened properties of concrete made of crushed aggregates containing no natural sand. Civil Engineering. Université Paul Sabatier - Toulouse III; Université Libanaise, 2021. English. ⟨NNT : 2021TOU30043⟩. ⟨tel-03343018⟩

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