دانلود رایگان مقاله حجم زیاد خاکستر بادی بتن: تاثیر عملی با دوز وفور کاهنده آب محدوده بالا

Abstract

The practice of using extraordinarily low water/binder ratio for high volume fly ash (HVFA) concrete mixes in order to realize adequate early strength is prevalent. Generally, superabundant dose of high range water reducer (i.e. superplasticizer) is required to make such mixes workable. The relationship between superabundant superplasticizer dose and various HVFA concrete properties is thus examined in this research work. Three groups of HVFA concrete mixes were designed for this purpose. Each group consisted of 3 mixes. Except for superplasticizer dose, the proportion of materials in the three group 1 mixes were the same, each mix containing 50% fly ash as replacement for cement. Of the three mixes, one contained maximum superplasticizer dose at 2% of binder by mass, the second contained superabundant dose at 3% while the third contained 4% dose. Group 2 and 3 mixes were similar to those of group 1 except that they contained 60% and 65% fly ash content respectively. Fresh concrete tests performed on the mixes included flow table and slump tests. Mechanical tests included compressive strength, splitting tensile strength, flexural strength and wear resistance tests. The outcome of the tests revealed that superabundant superplasticizer doses helped to obtain relatively lower water/binder ratios with good workability; led to reduction in wear/abrasion resistance; and had no observable relationship, beneficial or adverse, with the compressive, splitting tensile and flexural strengths of the HVFA concrete mixes. Increase in fly ash content was also noted to beget reduction in wear/abrasion resistance. In addition, the outcome indicated that increase in compressive strength does not necessarily translate to improved abrasion or wear resistance.

4. Conclusion

The conclusions that can be drawn from this study are as follows: 1) Superabundant superplasticizer dose has an adverse relationship with the wear resistance property of HVFA concrete. It can also be concluded that increase in fly ash begets reduction in wear resistance. 2) HVFA concrete with superabundant superplasticizer dose is not the best for applications like concrete pavement, concrete railway sleepers, warehouse floors etc. where abrasion resistance is highly essential 3) Superabundant superplasticizer dose, compared to prescribed dose, can help to achieve exceptionally low water/binder ratios with good fresh concrete properties in terms of flow and slump for HVFA concrete. 4) When superabundant superplasticizer dose is used, it appears the superplasticizing action per volume decreases as more dose is added. 5) Superabundant superplasticizer dose has no observable relationship, beneficial or adverse, with the compressive strength, flexural strength and splitting tensile strength of HVFA concrete. 6) If superabundant superplasticizer dose is used to achieve very low water/binder ratio for HVFA concrete mixes, the mixes can achieve good early and long term compressive strength. 7) High compressive strength does not necessarily translate to good abrasion resistance for HVFA concrete. 8) If superabundant superplasticizer dose is used to achieve very low water/binder ratio for HVFA concrete mixes, the mixes can meet the minimum 28-d flexural strength and 7-d splitting tensile strength of various standards. 9) The higher the fly ash content in HVFA concrete mixes, the higher the overall compressive strength becomes and the lower the overall flexural strength, splitting tensile strength and abrasion resistance become