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Abstract
High performance concrete is concretes with properties or attributes which satisfy the
performance criteria.
High performance concrete (HPC) is becoming the building material of choice for
many different applications, and it must be developed at the local level.
This research work presents the results of an experimental investigation. This
investigation aims to enhance mechanical properties and minimize shrinkage for high strength
concrete.
Several concrete mixtures using coarse/fme aggregate ratio of 1.8 were investigated. Variable examined in developing HPC mixtures’ includes silica fume (SF) content, water/cementitious materials ratios (W/Cm), and cement content. Additionally polypropylene fiber was used.
Silica fume was used as addition of type I Portland cement at contents ranging between 10 — 20 % by weight of cement content in the mixture. Use of super-plasticizer allowed a reduction of the water/cementitious materials ratio to 0.24 - 0.26 - 0.28, while the slump of fresh concrete was kept at a constant level of 120 ± 20 mm.
Several HPC mixtures, distinguished as having adequate workability and potential to
achieve 28 days’ áompressive strength up to 96 MPa at 28 days, were selected for this study.
The stages of the research project may be summarized as follows:
1. Establish an optimum cement, silica fume and super-plasticizer content to produce concrete with high strength and good workability.
2. Study the cube compressive strength development, at different ages, of concrete mixtures containing various levels of silica fume addition of Portland cement.
Compare the results with control mixture without silica fume.
3. Select an optimum silica fume/cement ratio based on compressive strength results.
4. Compressive strength, tensile strength, flexure strength, modulus of elasticity, plastic shrinkage, and drying shrinkage test were carried out at different ages.
5. Assess the adequacy of the AC! equations for predicting compressive strength, splitting tensile strength, flexural strength and modulus of elasticity of HPC made
with local materials.
6. Assess the utility of the water/cementitious materials (WICm) ratio for predicting HPC compressive strength.
7. Give some relations between compressive strength and other mechanical properties to predict these properties.
The effect of polypropylene fiber on the mechanical properties of high performance
concrete was studied.
Twelve reinforced concrete columns were tested in axial compression. The effect of
presence of polypropylene fiber, type of stirrups (either tie or spiral), and the size of stirrups
were examined.
The test results were tabulated and plotted through figures. Detailed discussions for
results were considered.
The study yields many conclusions for which,
— Using crushed dolomite, cement content of 600 kg/rn3, 10 % silica fume as addi’tion, and W/Cm ratio of 0.24 yields a 28 days cube compressive strength of
96.6 N/mm2.
— The use of 0.35 % of polypropylene fiber slightly decreases the cube compressive strength. The reduction percent ranges from 2 to 4 %.
— The use of polypropylene fiber is essentially in high strength concrete to decrease shrinkage and eliminate the negative effect of high cement content on shrinkage.
ACI 318 equation seems to provide a good prediction of the elastic modulus of high
performance concrete that has concrete compressive strength over 80 MPa