Fresh and mechanical properties of concrete made of binary substitution of millet husk ash and wheat straw ash for cement and fine aggregate

Now-a-days, many researchers use priceless industrial or agricultural products as the main raw material for the construction industry. However, these wastes are inexpensive and easily available everywhere to utilize for commercial purpose and also helpful in reducing the environmental pollution. This experimental study aimed to evaluate fresh (workability) and mechanical properties (density, permeability and split tensile strength, compressive and flexural strength) of concrete with 0%, 5%, 10%, 15% and 20% of millet husk ash (MHA) and 10%, 20%, 30% and 40% of wheat straw ash (WSA) to replace Ordinary Portland Cement (OPC) and sand respectively at conditions: a) concrete with MHA; b) concrete with WSA; and c) concrete with MHA and WSA. 525 concrete specimens were prepared with 1:1:2 mix proportions with 0.55 water/cement ratio and cured at 28 days. The increase of combined MHA and WSA contents to produce concrete decreased the workability of fresh concrete and decreased density and permeability of hardened concrete. Compressive strength, split tensile and flexural strength are increased with addition up to 15% of MHA and 30% of WSA combined. Same behavior is observed to compressive strength after chloride attack. Those results were better when compared to those of conditions a) and b). Therefore, it is possible to produce eco-friendly concrete with MHA replacing OPC and WSA replacing sand, individually or combined, which contributes to less environmental impact. (c) 2021 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

The effect of content and fineness of natural pozzolana on the rheological, mechanical, and durability properties of self-compacting mortar

Mineral admixtures are used in ordinary and self-compacting mortar to reduce carbon dioxide emission and enhance the performance of mortar at the fresh and hardened states. This paper reports the effect of the content and the fineness of natural pozzolana (NP) on rheological, compressive strength, total and autogenous shrinkage properties of self-compacting mortar. Capillary water absorption of self-compacting mortar was also investigated. Natural pozzolana was used as a partial cement replacement with two levels (15%wt. And 30%wt.) and ground to three specific surface Blaine (SSB) fineness measurements 350 m(2)/kg, 420 m(2)/kg and 500 m(2)/kg. Cement content, water to-binder ratio and superplasticizer content were kept constant for all self-compacting concrete mixtures. Rheological tests were conducted by measuring slump flow and V-funnel flow tests as well as using a rheometer to measure plastic viscosity and yield stress. Compressive strengths of self-compacting concretes were determined at 1, 7, 28, 56, 90 and 180 days of curing. Total and autogenous shrinkage were measured during three months and capillary water absorption of self-compacting mortar was also investigated after 90 days of water curing. The results indicated that the increase of replacement level of natural pozzolana affects negatively the rheological properties of self-compacting mortar. The same tendency is observed as the specific surface Blaine fineness increased. However, in the long-term (beyond 28 days of curing), the compressive strength of NP mixes exceeds that of control mortar. The increase of the fineness of natural pozzolana enhances compressive strength at later age but increases both the total and autogenous shrinkage compared with control mortar. It was observed that increasing the percentage of natural pozzolana generates an increase in water capillary absorption. However, increasing the fineness of natural pozzolana results in slightly lower water absorption of mortar