Effect of entrapped air on strength and durability of the concrete containing of chemical and natural admixtures

In order to use concrete as a building material with multiple applications, its mechanical and durability properties should be considered. Mechanical properties include compressive, tensile, flexural, and abrasive strength. And, the durability property, here, is defined as the resistance to sulfates and chlorides attacks. For all these situations, concrete porosity relates to the mechanical strengths and durability resistance in a specific way. In this study, these relations as well as the effect of chemical and natural additives; including Zeolite, Meta Kaolin, Micro Silica, and Plasticizers with different percentages; are investigated. To do this, specimens are compared in terms of temperature, concrete slump, porosity, permeability, electrical resistivity, water absorption, and compressive strengths of 7, 28, and 90 days. Results showed low levels of porosity for concretes with Micro Silica and Zeolite, respectively, high water absorptions for those with Meta Kaolin and Zeolite, respectively, and low levels of permeability for those of Micro Silica and Meta Kaolin, respectively. High electrical resistivity is found for the samples containing Meta Kaolin and Zeolite, after 7 and 28 days, and for the samples containing Zeolite and Micro Silica, after 90 days. Concrete samples containing Micro Silica and Meta Kaolin showed high levels of compressive strength. In this regard, although, Zeolite-concrete mixture had showed low level of compressive strength after 7 days, it was improved after more days. It is also concluded that a mixture of concrete with Micro Silica and 1.5% of plasticizer has the lowest level of porosity and the highest level of compressive strength. All these proved that, generally, reducing porosity improves mechanical and durability properties of concrete.