malek mohammad ranjbar taklimi

In this article, the ground granulated blast furnace slag and red mud, which are the waste products of iron and aluminum factories, were used as aluminosilicate base materials in the mix design of geopolymer repair mortar. The activation of base materials was done with a combination of sodium hydroxide solution (soda) and sodium silicate (water glass).The effect of steel fibers on compressive strength, toughness and drying shrinkage of mortar was investigated. Fiber mortars were used as a repair layer to retrofit brick beams. The results showed that the use of steel fibers in geopolymer mortar can effectively improve compressive strength and toughness, reduce drying shrinkage, and change the brittle fracture behavior of brick beams to a ductile behavior. The results of SEM-EDS test and measurement of Si/Al molar ratio indicated the existence of a three-dimensional and chained structure of geopolymer in the mortar microstructure. The conducted research is an effective and forward step in achieving geopolymeric products with an environmental and economic approach.

In this study, the bond strength between rebar and high-performance fiber-reinforced cementitious composites (HPFRCC) containing the combination of three types of steel fibers (1% and 2%), polypropylene and polyvinyl alcohol (0.1, 0.2, 0.3 and 0.4%) has been investigated at the temperature of the laboratory, 400 and 600 °C. For this purpose, at first, 19 specimens were constructed and evaluated for compressive strength testing under the mentioned temperatures, as the silica fume was considered 20% by weight of cement. Among the constructed HPFRCC, four superior mix designs were selected for investigating the bond strength between rebar and HPFRCC using pullout test. The results showed that the bond strength between rebar and HPFRCC samples containing 2% steel fibers with PP fiber in such a way that increasing the temperature up to 400 °C, decreased about 38%. while this reduction rate for the samples containing PVA fibers is about 26%, and this means that PVA fibers have a better performance than PP fibers in term of the bond between concrete and rebar when exposed to high temperatures. By increasing the temperature up to 600°c, the bond strength of rebar and HPFRCC continues to decrease until this drop is about 64% for selected samples containing fibers (2% steel and 3% PP) at the laboratory temperature (i.e., 23°c). The reduction for the HPFRCC sample containing 2% steel and 2% PVA fibers is calculated by 62%. The results of this study and the literatures indicated the effect of different parameters on the bond strength, so for further investigation, the bond strength modelled using artificial intelligence models. The results of rebar bond strength modeling in HPFRCC showed that the performance of the adaptive multivariate regression splines based on error statistical criteria was more accurate than the artificial neural network.

The utilization of recycled materials in the concrete industry has become one of the most essential environmental needs today, and more technical and economic studies are being performed every day in this subject. The effect of recycled materials on the shear behavior of geopolymer concretes was investigated in this work, along with a comparison to conventional recycled concretes and the effect of recycled aggregates on both concrete groups. For this purpose, ten mixing designs with recycled aggregate replacement percentages of 0, 25, 50, 75, and 100 were made in two groups of ordinary concrete and geopolymer concrete, as well as mechanical tests such as compressive strength, modulus of elasticity, and pull-off test. A reinforced beam without a shear element was also created for each mixing design to study the effect of this type of aggregate on the shear behavior of the beam. The findings revealed that increasing the percentage of recycled aggregates causes a loss in mechanical characteristics in the designs and a reduction in beam bearing capacity, indicating that geopolymer concrete has a higher replacement capacity than regular concrete.

In this paper, effects of curing methods (i.e. curing at ambient temperature (A), in oven (O) and in boiling water (BW)), NaOH solution concentration (i.e. 8 and 12 moles/liter) and disc thickness (i.e. 1, 2 and 3 cm) on pull-off strength (POS) of the geopolymer concrete containing Ground Granulated Blast Furnace Slag (GGBFS) and Natural Zeolite Powder (NZP) have been investigated. The results show that the value of the POS obtained from the 3 cm thickness disc is on average 2.6% higher than that obtained from the 2 cm thickness disc. This implies that the discs with thicknesses of 2 and 3 cm have given approximately equal values of the POSs. Moreover, the value of the POS obtained from the 2 cm thickness disc is on average 28.4% higher than that obtained from the 1 cm thickness one. Based on the results obtained from the 2 cm thickness disc: a) the ratios of the POSs of the samples cured in boiling water and oven to that of the specimen cured at ambient temperature have been obtained on average equal to 1.383 and 1.089, respectively. b) as 20% wt. of the GGBFS is substituted by the NZP, the value of the POS reduces by an average of 16.29%. c) as the NaOH solution concentration increases from 8 to 12 mole/liter, the value of the POS increases by an average of 14.48%. From the results, there is a strong nonlinear relationship between the compressive and pull-off strengths of the geopolymer concrete.

The main factor in integrated performance of repair overlay and substrate concrete is the bonding between them. The accurate measurement of bonding is dependent to factors such as strength and surface characteristics of substrate concrete, loading mechanism and curing condition of overlay. In this research, 8 mix designs are considered. For assessment of strength level and surface quality of substrate, two concrete grades in the ranges of 20-30 and 40-50 MPa, and also two surface conditions including simple finishing and ribbed finishing were considered. Repair overlays were considered from three different strength grades of self-compacting concretes contained 0.5% and 1% of steel fibers. After fabrication, for curing, three different conditions of curing in open air, curing in warm water, and standard curing were deemed. Compressive strength, flexural strength and splitting tensile strength tests were performed on samples, and Pull-Off method were used for evaluation of bonding strength. The results indicated that the impact of substrate strength on bonding is more significant than overlay strength, and also the effect of curing condition was more salient than finishing quality. The bonding strength of overlays contained 0.5% of steel fibers and with strength grades of C50, C60 and C70 cured in warm water were 105%, 108% and 104%, respectively, higher than same samples cured in open air.