Mix design requirements

　　Silica fume concrete mix design, mainly based on design requirements, to determine the silica fume incorporation method. The best dosage of silica fume, superplasticizer dosage and the optimal aggregate adjustment. Other design methods according to normal concrete.
First, the silica fume incorporation method

Mixed with silica fume in concrete, there are two general ways: First, within the mixed, second, Mixed, should be used in conjunction with the reducing agent.

Within the mixed method - instead of cement with silica fume, and is divided into equal parts instead of instead of two, instead of an equivalent substitute for the silica fume dosage equal to the amount of cement, silica fume instead of some place for the 1 ~ 3kg 1kg of cement, as a research general dosage is 5 to 30%, water-cement ratio generally remains the same.

Mixed method - as doped silica fume as admixtures in the concrete, that does not reduce the amount of cement mixed with silica fume conditions. Dosage is usually 5 to 10%. As the silica fume usage is different from the performance of concrete is not the same, Mixed method from the mechanical properties of concrete is much higher, but increased the amount of cementitious material in concrete.

Second, the optimal dosage of silica fume

　　Too little dosage of silica fume in concrete, not on concrete performance improvement, but too much ash, the concrete is too sticky, difficult construction, and the shrinkage deformation, frost resistance is poor, therefore, silica fume, should find the optimal dosage to get the best results. In general, dosage within 10% the effect is satisfactory. Silica fume used in the appropriate dosage is generally based on silica fume, cement type and aggregate properties, select the number of silica fume dosage, such as 3,5,7,10%, etc., forming the concrete specimens, drawing R-SF (strength - silicon powder dosage) curve to determine. It is noteworthy that the higher the price of silica fume, silica fume in determining the optimal dosage, they should also consider the technical and economic indicators.
Third, the optimal dosage of superplasticizer

Use of silica fume in concrete, if not mixed with water-reducing agent, want to maintain the same mobility, is bound to increase water consumption, increased water-cement ratio, silica fume concrete strength do not increase, this is not over silica promote the use of concrete in one of the reasons. Silica fume and superplasticizer in combination. Especially in combination with superplasticizer, silica fume mixed with water-cement ratio unchanged. Water does not increase, but also to achieve with non-silica fume concrete with the same fluidity. Silica fume concrete strength and other properties have been substantially improved.

Use of silica fume, are normally used for naphthalene superplasticizer, such as the construction of 1, H1, DH3, FDN, NF, N-B and so on. There melamine resin-reducing agent, widely used in Western Europe (called Melment). Melamine resin, water-reducing effect is good, generally 25% water reduction. However, domestic use is still low, mainly because of the high cost. Current liquid state, transportation inconvenience.

Naphthalene superplasticizer dosage in the silica fume concrete, plastic material is generally less than 1% of the amount, and some to reduce the water-cement ratio, mixing high-strength concrete, superplasticizer dosage of 2 to 3%.

Water-reducing agent for the selected species, type and materials used in concrete, used several dosage, such as 0.3,0.6,0.9,1.2%, measuring the slump of concrete (S), drawing slump - superplasticizer mixed volume curve, and consider the costs, determine the best dosage, but also to determine the superplasticizer dosage based on experience, for example, 10% silica fume, water-reducing agent for the H1 and UNF, the general dosage is 0.6% of the amount of plastic material so.