Long-term properties of special concrete with natural additive

Abstract

Present paper deals with the experimental study of high strength concrete with natural pozzolanic addition applied as Portland cement replacement. The motivation was to develop new type of high strength concrete with further application of environmental friendly materials. Natural pozzolans are silica-aluminous rocks which were successfully used in the ancient Rome as a component of hydraulic lime. Its high and regular porosity determines practical utilization as an adsorbent or filter agent. Performed experimental program is focused on the influence of natural pozzolan to the long-term properties. Studied additive was dosed as Portland cement replacement in doses of 10 %, 30 % and 50 % by weight. Evaluation of developed high strength concrete mixtures was realized on the base of determination of the bulk density, flexural strength, compressive strength, water absorption coefficient and de-icing salts resistance. The above named properties were investigated at the age of 28, 90 and 180 days. Gradual pozzolanic reaction caused expected increase of compressive strength of all studied mixtures. The highest increase by 25 % exhibited mixture with 10 % substitution. Concrete mixtures with higher cement substitution did not reach the properties of reference mixture. Water absorption coefficient values were negatively affected by the relatively high doses of studied additive of high porosity, but after 150 freeze-thaw cycles where not observed any deterioration of all studied mixtures. Based on the realized experimental program can be concluded the positive influence of natural pozzolan to long-term properties but its efficiency is very low. Substitution of Portland cement higher than 10 % by weight generally reduced mechanical properties below the level of reference mixture.