Optimization of Mix Proportion of High Performance Mortar for Structural Applications

Abstract

Problem statement: Mortar mix is a major construction material in fabrication of ferrocement structural elements. However, there have been scarce amount of technical data available on suitable mix proportion to achieve structural grade mortar with specific strength requirement and adequate level of workability for proper placement into construction formwork. Moreover, current practice in ferrocement construction work which uses mortar mix with cement: sand ratio ranging between 1:1.5 to 1:2 incurs high requirement of cement yet producing mix with suboptimum level of compressive strength. Approach: An experimental investigation was carried out to evaluate workability and compressive strength properties of structural grade mortar mixes with various cement: sand ratios ranging from 1:2.0-1:2.75 and varying water/binder ratio between 0.35 and 0.50. Throughout the laboratory investigation, a total of 28 batches of mortar mixes with various mix proportion were designed, cast and tested in accordance to relevant standards of practice prescribed by British Standard Institute (BSI) and American Society of Testing Material (ASTM). Results: At the end of the laboratory investigation program, high performance mortar mix with compressive strength exceeding 55 MPa and slump level within 50-90 mm which is suitable for heavy duty ferrocement construction work was successfully developed. Moreover, data on mix proportion for several other grades of mortar mixes ranging from grade 35 to grade 55 were also derived. Conclusion: It was found that optimum cement: Sand ratio of structural mortar is 1:2.25. With the use of this cement: Sand ratio in the production of structural grade mortar mix in fabrication of ferrocement structural elements, consumption of cement binder will be economized hence resulting in potential savings in term of material and production cost of mortar mix in the construction industry. Besides, it was also observed that strengths of mortar mixes do not vary linearly with cement content of the mix.