Durability of cellulose-cement composites assessed by accelerated testing under temperature and moisture variations - effects of blending by rice husk ash

More recent investigations on cellulose-cement composites predominantly deal with durability aspects, whereby use is made of accelerated weathering cycles as the main approach to establishing the deterioration mechanisms and the efficiency of treatment methods. As moisture transport is the main mechanism that leads to the deterioration of those composites, accelerated ageing tests are commonly based on wet-drying cycles with a combination of temperature and relative humidity (R.H.) variations. Both variables result in dimensional changes of the samples, leading to interfacial abrasion and the progressive decrease in the composites’ toughness and strength. To investigate the effects of each of these variables, the weathering tests were performed in an environmental chamber considering each variable separately in two ageing cycles. In the first one the composites were submitted to saturation and drying at a constant 25 °C, by means of a relative humidity change in the chamber. For the second ageing cycle a temperature variation between 20 °C and 60 °C at a constant R.H. of 50% was applied. The effects of each ageing cycle on the cellulose-cement composites were assessed on the basis of physical and mechanical parameters, determined after 0, 5, 20 and 50 cycles. Moreover, part of the samples was provided with electrical strain gauges, which rendered possible to determine the composites’ expansion-shrinkage behaviour during the temperature and R.H. variations. As the main treatment approach, the partial replacement of cement (OPC) by rice husk ash (RHA) was investigated. It was found that RHA improved the strength and durability performance of the composites, although the increased porosity resulted from the 30% replacement rate of OPC and carbonate filler by RHA.