14-05-2013, 12:24 PM
SELF COMPACTING CONCRETE
SELF COMPACTING.docx (Size: 869.56 KB / Downloads: 81)
INTRODUCTION
PROPERTIES OF SELF COMPACTING CONCRETE
Self-compacting concrete (SCC) has been described as "the most revolutionary devel-opment in concrete construction for several decades". Originally developed to offset a growing shortage of skilled labour, it has proved beneficial economically because of a number of factors, including:
• faster construction
• reduction in site manpower
• better surface finishes
• easier placing
• improved durability
• greater freedom in design
• thinner concrete sections
• reduced noise levels, absence of vibration
• safer working environment
Originally developed in Japan, SCC technology was made possible by the much earlier development of superplasticisers for concrete. SCC has now been taken up with enthu-siasm across Europe, for both site and precast concrete work. Practical application has been accompanied by much research into the physical and mechanical characteristics of SCC
The need for durable concrete in an aggressive environment leads automatically to con-crete with optimized mix composition and a low water/cement ratio. Such concrete may be difficult to compact and the risk of honeycombing, particularly in the cover concrete, increases. In addition, the quality and efficiency of compaction is extremely dependent on the person handling the vibrator. Hence, the better the concrete mix, from a durabili-ty point of view, the greater the risk of having inferior or bad compaction leading to re-duced quality in the final structure. With the aid of a range of chemical admixtures and the optimal grading of the aggregates, concrete with low water/cement ratio can be made to flow through complicated form geometry and around complex reinforcement layout without the use of vibrators. Flowing concrete will exert an increased pressure on the formwork, which must be taken carefully into account when designing the form-work. The use of SCC is also an environmentally friendly technology as the noise level from vibrators is almost eliminated because the concrete workers rarely need to work with vibrators, thus also eliminating the adverse effects the vibration of concrete has on the body (‘white fingers’).
PROPERTIES OF QUARRY DUST
In coming Days as natural sand sources decrease , rates increase, so the use of Quarry rock dust may be prove useful considering Economy and Durability. Common river sand is expensive due to excessive cost of transportation from natural sources and poses the problem of acute shortage in many areas . Its continued use has started posing serious problems with respect to its availability, cost and environmental impact. Also large-scale depletion of these sources creates environmental problems. Natural sand in many parts of the country is not graded properly and has excessive silt; on other hand quarry rock dust does not contain silt or organic impurities and can be produced to meet desired gradation and fineness as per requirement. Consequently, this contributes to improve the strength of concrete.
As environmental, transportation and other constraints make the availability and use of river sand less attractive, a substitute or replacement product for concrete industry needs to be found.
PROPERTIES OF QUARRY DUST
In coming Days as natural sand sources decrease , rates increase, so the use of Quarry rock dust may be prove useful considering Economy and Durability. Common river sand is expensive due to excessive cost of transportation from natural sources and poses the problem of acute shortage in many areas . Its continued use has started posing serious problems with respect to its availability, cost and environmental impact. Also large-scale depletion of these sources creates environmental problems. Natural sand in many parts of the country is not graded properly and has excessive silt; on other hand quarry rock dust does not contain silt or organic impurities and can be produced to meet desired gradation and fineness as per requirement. Consequently, this contributes to improve the strength of concrete.
As environmental, transportation and other constraints make the availability and use of river sand less attractive, a substitute or replacement product for concrete industry needs to be found.
RESEARCH SIGNIFICANCE
Quarry waste is generally considered as a waste material and causes an environmental load due to disposal problem. The successful utilization of quarry waste as fine aggre-gate would turn this waste material into a valuable resource. In addition, the strain in the supply of natural sand will be reduced, and the cost of concrete production will be offset if the quarry waste is used as a partial replacement of natural sand. However, it should be ensured that the incorporation of quarry waste does not harm the strength, and other key hardened properties and durability of concrete. More precisely, the quality of concrete should not be severely downgraded at the expense of cost reduction. Nevertheless, the non-destructive properties such as dynamic modulus of elasticity, ultrasonic pulse velocity, and initial surface absorption are useful to indicate the strength and durability of the concrete. Thus, this study provides some basis to judge the quality of flowing concretes incorporating quarry waste.
EXPERIMENTAL PROCEDURE
MATERIALS
Crushed granite stone, natural mining sand, quarry waste, ordinary (ASTM Type I) Portland cement, silica fume, Class F Malaysian fly ash, tap water, a sulfonated naph-thalene formaldehyde condensate-based superplasticizer, and an air-entraining agent were used to produce flowing concretes. Crushed granite stone and mining sand were used as coarse and fine aggregates, respectively. Quarry waste, obtained from a local aggregate quarry, was used as a partial replacement of mining sand. Both silica fume and fly ash were used in flowing concretes as a partial replacement of cement. Table 2.1 presents the major properties of the materials. In addition, the gradation of the aggre-gates has been shown in Figure 2.1.
4 Curing methods
Two types of curing were used. These were water and air curing. In water curing, the specimens were immersed under water. No lime was used to saturate the water. In air curing, the specimens were exposed to dry air. In both curing methods, the curing temperature was maintained at 20±2 oC. The cylinder specimens were cured until 7, 14, 28
and 56 days, whereas the cube specimens were cured until 28 and 56 days. Moreover, cube specimens were only subjected to water curing.
RESULTS AND DISCUSSION
Fresh properties
The fresh concrete properties determined were slump, slump flow, V-funnel flow and air content. In general, all fresh concretes exhibited the required level of flowability recommended for flowing concretes. The concrete mixtures produced the slump values from 230 to 245mm, slump flow from 520 to 550 mm and V-funnel flow in the range of 0.355 to 0.425 L/s. Flowing concretes generally provide a slump higher than 190 mm [1, 21], a slump flow greater than 500 mm [3, 4], and a V-funnel flow higher than 0.333 L/s [3]. Hence, all concretes possessed a good flowability. Besides, CQW concrete provided the highest values of 245 mm, 550 mm and 0.425 L/s for slump, slump flow and V-funnel flow, respectively.
SELF COMPACTING.docx (Size: 869.56 KB / Downloads: 81)
INTRODUCTION
PROPERTIES OF SELF COMPACTING CONCRETE
Self-compacting concrete (SCC) has been described as "the most revolutionary devel-opment in concrete construction for several decades". Originally developed to offset a growing shortage of skilled labour, it has proved beneficial economically because of a number of factors, including:
• faster construction
• reduction in site manpower
• better surface finishes
• easier placing
• improved durability
• greater freedom in design
• thinner concrete sections
• reduced noise levels, absence of vibration
• safer working environment
Originally developed in Japan, SCC technology was made possible by the much earlier development of superplasticisers for concrete. SCC has now been taken up with enthu-siasm across Europe, for both site and precast concrete work. Practical application has been accompanied by much research into the physical and mechanical characteristics of SCC
The need for durable concrete in an aggressive environment leads automatically to con-crete with optimized mix composition and a low water/cement ratio. Such concrete may be difficult to compact and the risk of honeycombing, particularly in the cover concrete, increases. In addition, the quality and efficiency of compaction is extremely dependent on the person handling the vibrator. Hence, the better the concrete mix, from a durabili-ty point of view, the greater the risk of having inferior or bad compaction leading to re-duced quality in the final structure. With the aid of a range of chemical admixtures and the optimal grading of the aggregates, concrete with low water/cement ratio can be made to flow through complicated form geometry and around complex reinforcement layout without the use of vibrators. Flowing concrete will exert an increased pressure on the formwork, which must be taken carefully into account when designing the form-work. The use of SCC is also an environmentally friendly technology as the noise level from vibrators is almost eliminated because the concrete workers rarely need to work with vibrators, thus also eliminating the adverse effects the vibration of concrete has on the body (‘white fingers’).
PROPERTIES OF QUARRY DUST
In coming Days as natural sand sources decrease , rates increase, so the use of Quarry rock dust may be prove useful considering Economy and Durability. Common river sand is expensive due to excessive cost of transportation from natural sources and poses the problem of acute shortage in many areas . Its continued use has started posing serious problems with respect to its availability, cost and environmental impact. Also large-scale depletion of these sources creates environmental problems. Natural sand in many parts of the country is not graded properly and has excessive silt; on other hand quarry rock dust does not contain silt or organic impurities and can be produced to meet desired gradation and fineness as per requirement. Consequently, this contributes to improve the strength of concrete.
As environmental, transportation and other constraints make the availability and use of river sand less attractive, a substitute or replacement product for concrete industry needs to be found.
PROPERTIES OF QUARRY DUST
In coming Days as natural sand sources decrease , rates increase, so the use of Quarry rock dust may be prove useful considering Economy and Durability. Common river sand is expensive due to excessive cost of transportation from natural sources and poses the problem of acute shortage in many areas . Its continued use has started posing serious problems with respect to its availability, cost and environmental impact. Also large-scale depletion of these sources creates environmental problems. Natural sand in many parts of the country is not graded properly and has excessive silt; on other hand quarry rock dust does not contain silt or organic impurities and can be produced to meet desired gradation and fineness as per requirement. Consequently, this contributes to improve the strength of concrete.
As environmental, transportation and other constraints make the availability and use of river sand less attractive, a substitute or replacement product for concrete industry needs to be found.
RESEARCH SIGNIFICANCE
Quarry waste is generally considered as a waste material and causes an environmental load due to disposal problem. The successful utilization of quarry waste as fine aggre-gate would turn this waste material into a valuable resource. In addition, the strain in the supply of natural sand will be reduced, and the cost of concrete production will be offset if the quarry waste is used as a partial replacement of natural sand. However, it should be ensured that the incorporation of quarry waste does not harm the strength, and other key hardened properties and durability of concrete. More precisely, the quality of concrete should not be severely downgraded at the expense of cost reduction. Nevertheless, the non-destructive properties such as dynamic modulus of elasticity, ultrasonic pulse velocity, and initial surface absorption are useful to indicate the strength and durability of the concrete. Thus, this study provides some basis to judge the quality of flowing concretes incorporating quarry waste.
EXPERIMENTAL PROCEDURE
MATERIALS
Crushed granite stone, natural mining sand, quarry waste, ordinary (ASTM Type I) Portland cement, silica fume, Class F Malaysian fly ash, tap water, a sulfonated naph-thalene formaldehyde condensate-based superplasticizer, and an air-entraining agent were used to produce flowing concretes. Crushed granite stone and mining sand were used as coarse and fine aggregates, respectively. Quarry waste, obtained from a local aggregate quarry, was used as a partial replacement of mining sand. Both silica fume and fly ash were used in flowing concretes as a partial replacement of cement. Table 2.1 presents the major properties of the materials. In addition, the gradation of the aggre-gates has been shown in Figure 2.1.
4 Curing methods
Two types of curing were used. These were water and air curing. In water curing, the specimens were immersed under water. No lime was used to saturate the water. In air curing, the specimens were exposed to dry air. In both curing methods, the curing temperature was maintained at 20±2 oC. The cylinder specimens were cured until 7, 14, 28
and 56 days, whereas the cube specimens were cured until 28 and 56 days. Moreover, cube specimens were only subjected to water curing.
RESULTS AND DISCUSSION
Fresh properties
The fresh concrete properties determined were slump, slump flow, V-funnel flow and air content. In general, all fresh concretes exhibited the required level of flowability recommended for flowing concretes. The concrete mixtures produced the slump values from 230 to 245mm, slump flow from 520 to 550 mm and V-funnel flow in the range of 0.355 to 0.425 L/s. Flowing concretes generally provide a slump higher than 190 mm [1, 21], a slump flow greater than 500 mm [3, 4], and a V-funnel flow higher than 0.333 L/s [3]. Hence, all concretes possessed a good flowability. Besides, CQW concrete provided the highest values of 245 mm, 550 mm and 0.425 L/s for slump, slump flow and V-funnel flow, respectively.