Durability Evaluation of Concrete with Multiadmixtures under Salt Freeze-Thaw Cycles Based on Surface Resistivity

According to the climatic characteristics of seasonal frozen area in northeast China, the concrete strength tests, surface resistivity, rapid chloride permeability, and freeze-thaw test under salt solution were carried out to study the influences of mineral admixtures and air content on the conventional properties and salt freeze-thaw resistance of concretes. Then, the correlation analysis of surface resistivity with strength and rapid chloride permeability were further investigated. Subsequently, the changes of cumulative mass loss and relative dynamic elastic modulus varying with salt freeze-thaw cycles were analyzed to study the influences of mineral admixtures and air content on salt freeze-thaw resistance of concrete. The test results showed that fly ash (FA) was not conducive to improve the strength and salt freeze-thaw resistance of concrete. However, blast furnace slag (BFS) and silica fume (SF) could improve the compressive and flexural strength of concrete, in which SF can improve its strength more significantly. Increasing the air content of concrete will lead to the reduction of its compressive strength, and the flexural strength first increased and then decreased. Nevertheless, the addition of air-entrainment agent (AEA) has the best effect on improving the salt freeze-thaw resistance of concrete. Moreover, surface resistivity of concrete has a good exponential function relationship with strength and a good power function relationship with rapid chloride permeability. Therefore, it is of great significance for engineering quality control and quickly and nondestructive testing.

Durability Assessment of Concrete with Class-F Fly Ash by Chloride Ion Permeability

This paper discusses on Rapid Chloride Permeability Test investigations on penetration of chloride ions included with replacement of cement by flyash material. By weigth of cement, the fly ash content is replaced from 0% to 60%. Concrete mixes with different binder content varies from 350, 400 and 450 kg/m3 were proportioned with different water binder(w/b) ratios = 0.4, 0.45 and 0.50. Specimens were casted and tested for 28 days. For all the combinations, RCPT was carried out and the charge passed through the specimens was noted. Rapid Chloride Permeability Test value of concrete without fly ash was found to be more than the concrete with fly ash. The Rapid Chloride Permeability Test values are found to be decreased if the percentage of flyash increases. The reason could be the pozzolanic reaction products (CSH) fill the pores between the cement pastes and cause a denser concrete matrix, resulting in better durability. Hence, it can be suggested that the fly ash concrete up to 50% replacement can be used for variety of applications.

Effects of Modified Metakaolin Using Nano-Silica on the Mechanical Properties and Durability of Concrete

This paper discussed the effects of modified metakaolin (MK) with nano-silica (NS) on the mechanical properties and durability of concrete. In the first phase, trial mixes of concrete were prepared for achieving the desired value of the 28 days compressive strength, and the charge passed in rapid chloride permeability test (RCPT). In the second phase, statistical analysis was performed on the experimental results using the response surface method (RSM). The RSM was applied for optimizing the mix proportions for the required performance by exploiting the relationship between the mix characteristics and the corresponding test results. A blend of 10% MK + 1% NS as part of cement replacement exhibited the highest mechanical properties and durability characteristics of concrete; concrete mix showed that the 28-days compressive strength (CS) was 103 MPa, which was 15% greater than the CS of the control mix without MK or NS. The same mix showed more than 40% higher flexural and split-tensile strength than the control mix; also it resulted in a reduction of 73% in the rapid chloride permeability value. ANOVA technique was used for optimizing the nano-silica and metakaolin content for achieving maximum compressive strength and minimum RCPT value. Statistical analysis using ANOVA technique showed that the maximum compressive strength and lowest RCPT value could be achieved with a blend of 10% MK and 1.55% NS.

FEASIBILITY OF UTILIZATION EAFD AS CEMENT REPLACEMENT IN CONVENTIONAL CONCRETE

— Industrial waste products can be considered as renewable resources, one of them is a steel manufacturing, which produced dust waste contain sponge iron, scrap metal and other steel wastes that impacted to environment. This waste material was called Electric Arc Furnace Dust (EAFD). This study investigates the feasibility of using EAFD as a cement replacement compared to silica fume (SF) and fly ash (FA) in terms of Chemical composition, workability, setting time, compressive strength and rapid chloride permeability resistance. The results showed that workability of EAFD is almost similar to control even if percentage of EAFD was increased. It is not refer to FA more workable or SF less workable with increase percentage of replacement. Furthermore, the EAFD significantly affect the setting time, which 3% EAFD replacement bring to prolong final setting time to more than 24 hours, while the setting time of SF and FA did not significant affected along with the increase replacement percentage. In addition, the 3% EAFD is optimum replacement for compressive strength and it is equivalent replacement level to 5% SF and 15% FA. Finally, the EAFD enhance the resistance for rapid chloride permeability more than FA but less than SF.