Experimental Study on Effects of Type and Replacement Ratio of Fly Ash on Strength and Durability of Concrete

Abstract

This paper presents the test results of a series of experimental studies on the effects of type and replacement ratio of fly ash on strength and durability of concrete. 3 types of fly ashes are used in this research, the specific surface area of which are 5070 cm2/g, 3760 cm2/g and 1970 cm2/g, respectively. They satisfy the requirement of Type-1, Type-2 and Type-4 fly ashes in Japanese Industrial Standard. Ordinary Portland cement, river sand, crushed sandstone, water reducer and air entraining agent are used as well. The results indicate that drying shrinkage of concrete is reduced when cement is partially replaced by fly ash. Comparatively, Type-2 fly ash's addition leads to a more effective drying shrinkage reduction, and those with replacement ratios result in larger dry shrinkage reduction. Carbonation increases with the increase of replacement ratio of fly ash, and concrete with Type-1 fly ash has higher carbonation than those with Type-2 and Type-4 fly ashes. The carbonation rate is found to be linear with water cement ratio regardless of replacement ratio of fly ash. Durability factor decreases with the replacement ratio of fly ash after 300 freezing and thawing cycles. Also, durability factor of concrete containing Type-1 and Type-2 fly ashes with replacement ratio of 25% to 55% is higher than 80%. However, those with Type-4 fly ash show lower durability factor after 300 cycles. Concretes with 70% replacement of fly ash are not durable in spite of the type of fly ash or specific surface area.

The Effects of Change in Fineness of Fly Ash on Air-Entraining Concrete

“…The maximum size was 5 mm, density in oven-dried condition was 2.60 g/cm 3 and absorption was 1.08 %.…”

“…Although more than 5 million tons of fly ash is generated from coal burning power stations in a year in Japan, the use of fly ash in concrete is still limited, because of difficulty in quality control of air-entraining fly ash concrete [1][2][3][4]. Japanese Industrial Standard, JIS A 6201, 'Fly ash for Use in Concrete' [5], specifies 4 types of fly ash depending on fineness, ignition loss, flow value ratio and activity factor as shown in Table 1.…”

Properties of a Composite Cement Binder Using Fuel Ashes

“…At the same time, ashes in cement binders may exhibit plasticizing and water-holding capacity [14][15][16]. The strength of cement concrete with the ashes was found to be more dependent on the specific surface area of the ashes [17][18][19].…”

Experimental Study on Durability Improvement of Fly Ash Concrete with Durability Improving Admixture

“…The main reasons are as follows. (1) The quality of fly ash is unstable because the quality of fly ash changes greatly with that of coals [ 11 , 12 ]; (2) there is lower early age compressive strength of concrete due to lower activity of fly ash [ 13 , 14 ]; (3) pozzolanic reaction of fly ash leads to decreased pH value of concrete, which results in a poor carbonation resistance [ 15 – 17 ]. In addition, in order to ensure the resistance of freezing-thawing action, it is necessary to entrain a certain amount of air in the concrete.…”