Effect of Nano Silica De-agglomeration, and Methods of Adding Super-plasticizer on the Compressive Strength, and Workability of Nano Silica Concrete

Abstract

Nowadays, nano silica appears to be one of the attractive cement substitution alternatives for researchers. Several authors have studied the physical effects of its incorporation on cement, despite of significant inconsistencies in reported results, specially workability and compressive strength of resulting concrete. This paper presents a thorough experimental investigation testing more than 16 concrete mixtures, which covers some of the main reasons of these inconsistencies. One of these problems is the method of applying the nano particles, as they are highly agglomerated, and if applied directly in a bulk composite, they often lose their high-surface area due to grain growth or unavailability of the high surface area where it matters. The presented research investigated how agglomeration can affect the compressive strength, and workability of normal strength concrete. Different methods of de-agglomeration were tested, as sonication, homogenization, and stirring. Besides, optimization of the super plasticizer's addition timing to concrete incorporating nano silica (NS) is elaborately investigated by adding the superplasticizer in different timings of addition; starting by adding NS to superplasticizer and water then applying de-agglomeration method, ending with de-agglomeration of NS alone with portion of water, then adding SP to the other portion of water before application them to the dry components. Results showed that sonication proved to be the most significant de-agglomeration method as it enhanced the gain in compressive strength of concrete by 23% by using only 1% nano silica as cement substitution. Sonication of NS also helped increasing the concrete workability significantly as a result of better dispersion of NS. As for the superplasticizer addition time, sonication of NS alone with portion of water, then adding SP to the other portion of water before application them to the concrete dry components showed a significant performance as compared to the other timings, as the compressive strength reached an increase of 26% compared to the control specimens.

Keywords: Nano silica, concrete, plasticizers, agglomeration, workability, strength.