The main object of this work is to evaluate the possibility for using reasonable cement content a... more The main object of this work is to evaluate the possibility for using reasonable cement content and fine materials to reduce costs of expensive chemical admixtures needed for the manufacturing of self-compacting concrete (SCC). In this work, three values of cement content are used (rich, medium and lean mixes) with cement content of 400, 300 and 250 kg/m 3 respectively. Two maximum aggregate sizes of (10 and 20mm) for each cement content are used. The powder content material is (cementations + filler) is maintained constant (500kg/m 3) while the W/cm ratio ranges from 0.43 to 0.68. 10% Reactive Metakaolin Class N is used as a partial replacement by weight of cement. On the other hand, limestone dust was used as a partial replacement by weight of the powder content Tests were carried out on all mixes to obtain the properties of fresh concrete in terms of viscosity and stability. The results showed that increasing the percentage of filler (limestone dust) from 20% in rich mixes to50% in lean mixes of the total weight of the powder content reduces the amount of cement in SCC without significant effect on the fresh properties of the SCC mixes. This conclusion is significant from the economical point of view. The mechanical properties of hardened SCC mixes are also assessed. (compressive strength, modulus of elasticity). The results obtained from this work show that it is possible to produce SCC with different levels of cement content (250 to400kg/m 3) using local available materials which satisfy the requirements of this type of concrete .The test data collected indicate that these materials can be used in the manufacturing of economical SCC.
ABSTRACT Contamination of aggregates with sulfate salts (especially gypsum) is a major problem in... more ABSTRACT Contamination of aggregates with sulfate salts (especially gypsum) is a major problem in Middle East concrete construction. Fine aggregate has more detrimental effect due to its large surface area (fineness). An experimental work had carried out to investigate the behavior of high performance concrete exposed to internal sulfate attack in comparison with traditional concrete. Four sulfate contents (0.5, 1.5, 2.0, and 2.5 %) in fine aggregate were studied. Metakaolin was used as a pozzolanic material, which has proved itself as a good active one. Teasing program included compression, splitting, and ultrasonic pulse velocity tests. 168 cubes and 216 cylinders were cast throughout this program. The test period was extended to 210 days. The harmful effect (reduction in strength) of sulfate was obvious in early ages in contrast to external attack (as early as 7 days). The reduction in strength was continuous and higher in later ages and for higher SO 3 contents with reference to the mix with 0.5% SO 3 . Test results showed that high performance concrete had lost strength, in such an environment, but it was more resistant than normal concrete and it may gain strength with age due to the pozzolanic action of metakaolin. The ultrasonic velocity results were positively proportional to strength development but with a slower rate of variation.
ABSTRACT The ACI Committee 209 (ACI 209R- 97) had presented a model for prediction of concrete sh... more ABSTRACT The ACI Committee 209 (ACI 209R- 97) had presented a model for prediction of concrete shrinkage. The included variables in this model are related to mix proportions, member geometry, curing method, and age of concrete. The predictions of this model had not pay adequate attention to the effect of the coarse aggregate on restraining shrinkage strain of concrete and overestimate the shrinkage half- time especially in hot climates. A parametric study was done to investigate the effect of variables other than those included in the ACI model (concrete and aggregate stiffness, aggregate volume, actual added water). Three types of normal-weight aggregate and one light-weight aggregate were included with two moisture conditions (dry and saturated). Teasing program included length change, compression, splitting tensile and static modulus of elasticity tests. The test period for shrinkage strain was extended to 150 days. A mathematical model based on dimensional analysis was built according to current experimental data. The predictions of this model stick close to the actual results (R2= 0.97) and it proves itself as a good tool to predict concrete shrinkage strains at anytime after curing is ceased. Another model was built to calculate shrinkage half-time. This factor is defined as the end of short-term age of concrete shrinkage. Finally, a proposed procedure for ultimate shrinkage prediction was suggested and it was verified reliable throughout statistical tests.
The main object of this work is to evaluate the possibility for using reasonable cement content a... more The main object of this work is to evaluate the possibility for using reasonable cement content and fine materials to reduce costs of expensive chemical admixtures needed for the manufacturing of self-compacting concrete (SCC). In this work, three values of cement content are used (rich, medium and lean mixes) with cement content of 400, 300 and 250 kg/m 3 respectively. Two maximum aggregate sizes of (10 and 20mm) for each cement content are used. The powder content material is (cementations + filler) is maintained constant (500kg/m 3) while the W/cm ratio ranges from 0.43 to 0.68. 10% Reactive Metakaolin Class N is used as a partial replacement by weight of cement. On the other hand, limestone dust was used as a partial replacement by weight of the powder content Tests were carried out on all mixes to obtain the properties of fresh concrete in terms of viscosity and stability. The results showed that increasing the percentage of filler (limestone dust) from 20% in rich mixes to50% in lean mixes of the total weight of the powder content reduces the amount of cement in SCC without significant effect on the fresh properties of the SCC mixes. This conclusion is significant from the economical point of view. The mechanical properties of hardened SCC mixes are also assessed. (compressive strength, modulus of elasticity). The results obtained from this work show that it is possible to produce SCC with different levels of cement content (250 to400kg/m 3) using local available materials which satisfy the requirements of this type of concrete .The test data collected indicate that these materials can be used in the manufacturing of economical SCC.
ABSTRACT Contamination of aggregates with sulfate salts (especially gypsum) is a major problem in... more ABSTRACT Contamination of aggregates with sulfate salts (especially gypsum) is a major problem in Middle East concrete construction. Fine aggregate has more detrimental effect due to its large surface area (fineness). An experimental work had carried out to investigate the behavior of high performance concrete exposed to internal sulfate attack in comparison with traditional concrete. Four sulfate contents (0.5, 1.5, 2.0, and 2.5 %) in fine aggregate were studied. Metakaolin was used as a pozzolanic material, which has proved itself as a good active one. Teasing program included compression, splitting, and ultrasonic pulse velocity tests. 168 cubes and 216 cylinders were cast throughout this program. The test period was extended to 210 days. The harmful effect (reduction in strength) of sulfate was obvious in early ages in contrast to external attack (as early as 7 days). The reduction in strength was continuous and higher in later ages and for higher SO 3 contents with reference to the mix with 0.5% SO 3 . Test results showed that high performance concrete had lost strength, in such an environment, but it was more resistant than normal concrete and it may gain strength with age due to the pozzolanic action of metakaolin. The ultrasonic velocity results were positively proportional to strength development but with a slower rate of variation.
ABSTRACT The ACI Committee 209 (ACI 209R- 97) had presented a model for prediction of concrete sh... more ABSTRACT The ACI Committee 209 (ACI 209R- 97) had presented a model for prediction of concrete shrinkage. The included variables in this model are related to mix proportions, member geometry, curing method, and age of concrete. The predictions of this model had not pay adequate attention to the effect of the coarse aggregate on restraining shrinkage strain of concrete and overestimate the shrinkage half- time especially in hot climates. A parametric study was done to investigate the effect of variables other than those included in the ACI model (concrete and aggregate stiffness, aggregate volume, actual added water). Three types of normal-weight aggregate and one light-weight aggregate were included with two moisture conditions (dry and saturated). Teasing program included length change, compression, splitting tensile and static modulus of elasticity tests. The test period for shrinkage strain was extended to 150 days. A mathematical model based on dimensional analysis was built according to current experimental data. The predictions of this model stick close to the actual results (R2= 0.97) and it proves itself as a good tool to predict concrete shrinkage strains at anytime after curing is ceased. Another model was built to calculate shrinkage half-time. This factor is defined as the end of short-term age of concrete shrinkage. Finally, a proposed procedure for ultimate shrinkage prediction was suggested and it was verified reliable throughout statistical tests.
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