THE APPLICATION OF RESPONSE SURFACE METHODS (RSM) TO STUDY THE EFFECT OF PARTIAL PORTLAND CEMENT REPLACEMENT USING SILICA FUME ON THE PROPERTIES OF MORTAR

The addition of pozzolan material, such as silica fume in order to improve mortar or concrete quality has been reported in many papers. However, the previous experimental design was only limited to factors that had a significant influence on the response. In addition, the results of the research analysis are only able to determine differences between the levels of factors and show the maximum or minimum response values, limited to the level of factors planned only. Response Surface Method used in the experiment of this study can analyze the problems of several independent variables that affect the response variable. The basic idea of this method is to use experimental design involving statistics to find the optimal value of the effect of adding silica fume as a partial substitute material for mortar to the compressive strength resulted. The design of the experimental proportion in this study was carried out by replacing 20% silica fume in cement as the middle boundary. Furthermore, the proportion of silica fume, cement and sand is reduced in number to the lower limit and added to the upper limit of the experimental design. Conclusions achieved; 1) Analysis using the Response Surface Method shows the optimal composition of mortar mixture obtained by adding 23.6% silica fume to cement, so that the optimal compressive strength test is at 55.8 MPa. 2) The optimal composition can also reduce the absorption of mortar to water, which only absorbs 5.34% water compared to mortar without silica fume which absorbs water up to 8.84%. 3) Addition of silica fume to mortar can increase 1.33% pH of mortar. The pH of the mortar with the addition of silica fume remained in alkaline conditions 9.75.