Effect of mixture proportions on the drying shrinkage and permeation properties of high strength concrete containing class F fly ash

Sustainability of concrete can be improved by using large volume of fly ash as a replacement of cement and by ensuring improved durability of concrete. Durability of concrete containing large volume of class F fly ash is dependent on the design of mixture proportions. This paper presents an experimental study on the effect of mixture proportions on the drying shrinkage and permeation properties of high strength concrete containing large volume local class F fly ash. Concrete mixtures were designed with and without adjustments in the water to binder ratio (w/b) and the total binder content to take into account the incorporation of fly ash up to 40% of total binder. Concretes, in which the mixture proportions were adjusted for fly ash inclusion achieved equivalent strength of the control concrete and showed enhanced properties of drying shrinkage, sorptivity, water permeability and chloride penetration as compared to the control concrete. The improvement of durability properties was less significant when no adjustments were made to the w/b ratio and total binder content. The results show the necessity of the adjustments in mixture proportions of concrete to achieve improved durability properties when using class F fly ash as a cement replacement

Thermal properties and residual strength after high temperature exposure of cement mortar using ferronickel slag aggregate

This study evaluates the thermal properties of cement mortar using by-product ferronickel slag (FNS) fine aggregate and its residual strength after high temperature exposure. Compressive strength of mortar increased when FNS was used up to 50% replacement of sand and then reduced with further increase of FNS. Volume of permeable voids (VPV) increased by 4% and 7% respectively for using 50% and 100% FNS fine aggregate. Thermal conductivity of mortar decreased from 2.34 W/m.K for using 100% sand to 1.65 W/m.K and 1.16 W/m.K for 50% and 100% FNS, respectively. Similarly, specific heat increased from 2.18 MJ/m3.K to 2.43 MJ/m3.K for 100% replacement of sand by FNS. These changes of VPV and thermal properties are attributed to the cavity of FNS particles, and their larger size and angular shape. Residual strengths of mortar after exposure to 800 °C were found marginally less for using FNS aggregate. This is attributed to the decrease of thermal conductivity of mortar by FNS. Overall, FNS aggregate showed improved thermal insulating properties and thermal mass of mortar without compromising compressive strength. Therefore, FNS can be considered for use as an energy efficient sustainable building material