Effects of Physical and Chemical Treatments of Silica Fume on the Strength and Microstructures of Mortar

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Title: Effects of Physical and Chemical Treatments of Silica Fume on the Strength and Microstructures of Mortar

Author(s): S. Nagataki, N. Otsuki, and M. Hisoda

Publication: Special Publication

Volume: 149

Issue:

Appears on pages(s): 21-36

Keywords: agglomeration; compressive strength; durability; high-performance concretes; microstructure; mineral admixtures; mortars (material); porosity; silica fume; strength; superplasticizer; workability; Materials Research

Date: 10/1/1994

Abstract:
Recently, there has been a great demand for high-quality concrete and concrete structures with high performance. In this context, silica fume is one of the most remarkable mineral admixtures that can give concrete high performance, such as high workability, strength, and durability. However, it is unclear as to the types of form silica fume takes in concrete, mortar, and cement paste. Some researchers point out that silica fume may be in high agglomeration. Therefore, it is very important to disperse silica fume in concrete effectively to get high-performance concrete. Consequently, this paper deals with the effect of physical treatment (ultrasonic homogenizer) and chemical treatment (superplasticizer) of silica fume on the properties of mortar. In this study, different silica fumes were used, one Japanese and five imported. The investigated properties of mortar were workability (flow values), compressive strength, and total pore volume. The study resulted in the following conclusions: 1) Silica fumes in the Japanese market were highly agglomerated in the natural state. This agglomeration of silica fume can be broken up by using some treatment methods, such as ultrasonic homogenizer and superplasticizer. 2) Physical treatment (ultrasonic homogenizer) before mixing mortar was useful to improve compressive strength and to decrease total pore volume of mortar containing silica fume. The use of superplasticizer could result in highly workable mortar. 3) The effectiveness of ultrasonic homogenizer treatment and that of superplasticizer treatment are different.