Mechanical Properties of Ultra High Performance Concrete

Abstract

UHPC (ultra-high performance concrete) is a relatively new type of concrete that exhibits mechanical properties that are far superior to those of conventional concrete and in some cases rival those of steel. The main characteristics that distinguish UHPC from conventional reinforced concrete are the improved compressive strength, the tensile strength, the addition of steel fibers, and the resistance to corrosion and degradation. In this work an original UHPC was modified through partial replacement of cement by silica sand powder with varies percentage (0% , 12.5% , 25%), and partial replacement of natural sand by silica sand with varies percentage (0% , 50% , 100%) as fine aggregate.

The research included a significant experimental phase, the experimental phase focused on determining the material behaviors of UHPC from the testing of (648) individual specimens towards determining,(compressive strength, , splitting tensile strength, flexural strength, water absorption, and modulus of elasticity).

108 cubes ( 50*50*50 mm) are for compressive strength test , 108 prisms (40*40*160 mm) are for flexural strength test , 108 cylinders (75*150 mm) are for splitting tensile strength test , 216 cubes ( 50*50*50 mm) are for water absorption test, and 108 cylinders(150*300 mm) for static modulus of elasticity.

The mixes composition in this study consists of ordinary portland cement (average size 15µm), fine sand (average size 150- 600µm), silica fume(average size 0.15µm), silica sand (average size 150- 600µm), powder of silica sand(average size 10µm),water, superplasticizer and accelerator. All the specimens were under (20)Cº water cured for (3, 7, 14, 28) days.The steel fiber was neglected in this work. The results were up to (128.6 MPa) for compressive strength, up to(30.4 MPa) for flexural strength, up to (7.2 MPa) for splitting tensile strength, up to (44.6 GPa) for modulus of elasticity,and (0.032 kg/m²) for water absorption at (28) days age.

Finally, it was found that even 25% of cement was replaced by silica sand powder, compressive strength was not suffered, and even 50% of natural sand was replaced by silica sand, compressive strength , flexural strength , splitting tensile strength and modulus of elasticity were increased about (9% , 16.9% , 33.3% , 16.7%) respectively compared with mixture of 100% natural sand.