Abrasion resistance and compressive strength of unprocessed rice husk ash concrete

This paper investigates the effects of adding natural rice husk ash collected from uncontrolled burning and without previous grinding (NRHA) as cement replacement in concrete. To obtain an adequate particle size, NRHA was mixed with coarse aggregate for a convenient period of time before adding the other components. Compressive strength, water absorption, porosity, and abrasion resistance expressed as weight loss were examined. Test results show that decreasing the particle size through mixing with coarse aggregate improved the compressive strength, reduced the permeability, and increased the abrasion resistance of concrete. By mixing NRHA with aggregate for 8 min, abrasion resistance improved by 10.35 and 23.62% over the control concrete at 28 and 91 days, respectively. Incorporating NRHA in concrete by grinding with coarse aggregate during the mixing process could be suitable for making normal-strength concrete and for applications where abrasion resistance is an important parameter. In addition, using NRHA as a partial replacement cement contributes to the reduction of CO2 emissions due to the production of cement

Properties of eco-friendly cement mortar contained recycled materials from different sources

Building materials such as sand, cement, bricks, and steel are usually the main components of the construction sector. All these materials are produced from existing natural resources and they will cause substantial damage to the environment as a result of their continuous depletion. Moreover, during the manufacture of various building materials, especially cement, a high concentration of carbon dioxide is constantly emitted into the atmosphere. Therefore, to reduce this environmental damage as well as to save natural resources, this study was performed to recycle the wastes of some of building materials such as marble, granite and porcelain tiles and clay brick through using them as cement and aggregate replacement materials in cement mortar. Sixteen mixtures were cast for this study. In addition to the control, the mortar mixes were divided into five groups, three mixes in each group. In four of the five groups, cement was replaced in three proportions (5%, 10%, 15% by weight) with each of marble, granite, porcelain and clay brick waste powders (passing through 150-μm sieve). The fifth group included 100% replacing (by weight) of the natural sand with the marble, granite and porcelain tiles wastes (with a comparable gradation). The influence of these wastes on flow rate, compressive strength, flexural strength, bulk density, ultrasonic pulse velocity (UPV) and water absorption tests were observed. Results showed that it is possible to produce an eco-friendly mortar made with 100% recycled marble or porcelain aggregate with a significant improvement in the mechanical and durability properties in comparison with natural aggregate mortar

Effects of silica fume fineness on mechanical properties of steel fiber reinforced lightweight concretes subjected to ambient and elevated temperatures exposure

This paper presents the effects of silica fume (SF) fineness and fiber aspect ratios of steel fiber on fresh and harden characteristics of high-strength lightweight concrete containing oil palm shell as coarse aggregates. The effect of elevated temperatures on the residual compressive strength of above concretes is also evaluated in this study. Three different SF fineness of 18400, 21000, and 28000m 2 /kg and 2 different aspect ratios of steel fiber of 40 and 80 are considered. Results show that the increase in SF fineness and steel fiber aspect ratio marginally affect the air-dry density of steel fiber reinforced lightweight high-strength concretes, however, the workability is reduced by about 9% to 14% due to increase in SF fineness. The compressive strength of steel fiber reinforced lightweight concretes at all age increases with increase in SF fineness and an improvement of about 37% is observed at 56days by increasing the SF fineness from 18400 to 28000m 2 /kg. Strong correlations are also observed between the strength improvement factor and the SF fineness. Water absorption of above concretes is also reduced by 3% to 14% due to increase of SF fineness from 18400 to 21000 and 28000m 2 /kg. The increase of SF fineness also significantly reduces the residual compressive strength loss at 300°C and 450°C. This loss of residual compressive strength is lower in lightweight concretes containing 16mm long steel fiber than 8 mm long steel fiber. The existing Eurocode model overestimates the residual compressive strength of steel fiber reinforced lightweight concretes containing no SF, however, this discrepancy is significantly reduced with increase in SF fineness