Influence of aggregate and supplementary cementitious materials on the properties of hydrated lime (CL90s) mortars (original) (raw)
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Journal of Materials in Civil Engineering, 2014
This paper studies the effect of rice husk ash (RHA) in the properties of hydrated lime (calcium lime-CL90s) mortars with a view to improve their properties and make them more sustainable. The variation in mortar properties was related to the activity of the RHA, which was assessed by measuring its specific surface area, fineness, reactivity, composition, and amorphousness. According to the results, the RHA investigated is a low-temperature, highly reactive ash of high specific surface area that contains crystalline silica and unburnt cellulosic material and was probably produced between 400 and 500°C. Pozzolanic hydrates were clearly present after 24 h, progressively increasing in size and amount (at 3 and 7 days) and linking to each other to form continuous networks after 14 days. The paper concludes that lime replacement by RHA improves mortar workability, lowering water/binder ratio and the amount of water required to reach a specific consistency. RHA also enhances bulk density and lowers the difference between real and bulk densities thus resulting in lower porosity. Lime replacement by RHA enhances strength, and accelerates setting and early strength gain. Finally, with increasing RHA content, lime mortars become progressively stiffer and more elastic, yet remain plastic and thus undergo significant strain before failure.
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This study aims to investigate the hydration and strength characteristics of green cementitious mortars with ultrahigh-volume limestone-calcined clay as well as two kinds of Class F fly ash. Using the ASTM C311 strength activity index test method, the effect of different pozzolan replacement levels of cement (0%, 20%, 50%, and 80%, by weight) were investigated. Compressive strength at 3, 7, 14, 28 and 90 days under standard curing was recorded, and hydration heat of the 20% and 80% replacement mixes was studied using iso-thermal calorimetry. It was observed that the effectiveness of the pozzolan in mortars depends on particle size distribution, glassy or amorphous nature, surface area and replacement level. The sum of all these effects can be captured by the strength activity test only if the standard recommended 20% pozzolan mix is substituted with the actual mix composition. The results in this study provide insights into the mix design and applications of ultrahigh-volume pozzola...
Impact of Aggregate Type on Air Lime Mortar Properties
Energy Procedia, 2014
In recent years, the need for low energy materials has become increasingly recognised. Government targets aim to achieve a decrease in carbon emissions by 80% before 2050. With the construction industry being responsible for approximately 50% of UK carbon emissions, an increased use of low energy materials could go a long way to achieving this target. With this in mind, it is also important that materials still have adequate properties to fit their purpose. For this study, four limestone aggregates were compared with a silicate aggregate in order to assess the impact of the aggregate type on the properties of air lime mortar (CL90). The primary focus was to assess the differences in compressive strength, and investigate reasons behind the measured differences. Without exception, the mortars made with limestone aggregate have higher compressive strengths than those made with silicate sand. Phenolphthalein staining shows slight differences in carbonation levels at 28 days, which could help to explain the strength differences observed. Furthermore, SEM analysis has revealed differences at the binder/aggregate interface between limestone aggregate mortars and silicate sand mortars.
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Hardening of calcium hydroxide and calcium silicate binders composed of cement, rice husk ash (RHA) and lime in different compositions were studied with mortars using thermal analysis, mechanical strength and SEM. When cement is partially replaced with RHA and lime, hardening occurs as a result of combined hydration, pozzolanic reaction and carbonation reaction. While hydration of cement contributes to the early strength development of the mortars, carbonation is much more pronounced at later stage with the decrease in the cement content and increase in the porosity of the mortars. RHA-cement mortars indicated a long-term strength development, which is lower than that of the reference cement mortar. This was attributed to their higher porosity due to the high water demand of the porous RHA grains. Strength reduction was recorded at the very early stage for RHA-cement-lime mortars containing 10%-wt cement as well as RHA-lime mortars. This has been explained with the insufficient ceme...