Use of micro and nano volcanic scoria in the concrete binder: Study of compressive strength, porosity and sulfate resistance

This paper aims to investigate the effect of volcanic scoria (VS) when added at micro or nano level on some concrete properties. Syria is rich in volcanic scoria with estimated reserves of nearly 1 billion tonnes. Three concrete properties, namely compressive strength, porosity and sulfate resistance, have been examined. Six percentages of micro-VS ranging from 0% to 50%, and nano-VS ranging from 0% to 5% have been used in making the investigated concretes. Test results revealed that the low early compressive strength of micro-VS-based concretes could be overcome by grinding VS to a nano size. In addition, significantly improved durability properties were obtained when VS was used either at micro or nano level. Much lower porosity and expansion values were clearly noted in the VS-based concretes. The efficiency factor (k) using the Bolomey equation and the durability indicator were evaluated to compare the behaviour of the VS-containing concrete with the reference concrete. The efficiency factor decreased with the increase of micro-VS/binder ratio and increased with the increase of nano-VS/binder. The calculated durability indicators showed that micro-VS content of 30% and nano-VS contents of 3 and 4% had approximately the highest indicator values. The replacement level of 30% at micro level and (3 & 4)% at nano level met k value of about 0.44 and 6, respectively, which would be useful for the designers of concrete mix. Based on the analyzed data, some relationships among the investigated properties were extracted. Further, scanning electron microscopy (SEM) technique and thermal gravity analysis (TGA) were employed in the current study to observe the resulting modifications in the microstructure of some VS-containing pastes. Large crystals of ettringite were observed in the pastes containing VS0 versus much smaller ones in the 3% nano-VS containing paste, after 52 weeks of exposure to 5% Na2SO4.