The main purpose of this study was to investigate the compressive strength and microstructure characteristic of alkali-activated metakaolin cement (AAMC). In accordance with this purpose, besides the pure metakaolin activation five other mixtures were designed by substitution of different OPC ratios instead of metakaolin (MK) from 0 to 25 (5, 10, 15, 20, 25% OPC). AAMC was activated with sodium silicate (Na2SiO3) of modulus Ms = SiO 2 /Na2O = 3.1 and NaOH solutions (32% of NaOH, 68% of water by mass). The ratio of liquid/solid (L/S) was kept constant at 0.65. All specimens were cured at 70 °C for 72 hours then kept in room conditions until the days that experiments were performed. Compressive strength and UPV experiment tests were carried out on all specimens at different curing periods of 3,14,28 and 90 days. In addition, the microstructure of 28 days alkali-activated metakaolin cements were analyzed with scanning electron microscope (SEM). The results showed that AAMC specimens reached the desired strength and major part of the final strength was gained at the end of 3 days of curing.
This study reports the results of high temperature effects on the properties of steel fiber reinforced self-compacting concrete (SFRSCC) fabricated by replacing cement with ground pumice powder (GPP) as mineral additive at different substitution rates. The mixtures had the same amounts of steel fiber and the binding material with constant water to binder (w/b) ratio of 0.37. In this context, five SFRSCC series were prepared by replacing Portland cement (PC) with 5, 10, 15, and 20% of GPP including the control mix. Sixty cube samples with a dimension of 150 × 150 × 150 mm were fabricated and exposed to curing aged 3, 7, 28, and 90 days to conduct compressive strength tests and a total of 100 × 100 × 350 mm 18 beam samples cured at 28 days were fabricated to perform the flexural strength tests. Durability tests were performed on the 18 cube samples of 100 × 100 × 100 mm subjected to water curing at 28 days. In addition, the relation between the compressive strength and Ultrasonic Pulse Velocity (UPV) of SFRSCC samples was compared aged 1, 3, 14, and 28 days. Samples of SFRSCC were subjected to the temperatures of 200, 400, 600, and 800 C after being cured at 28 days then cooled to room temperature before conducting tests. The results revealed that the compressive strength of all SFRSCC mixes enhanced at 200 C by 5.34 and 3.55% for control and GPP10 mixes respectively. The strength loss of mixes incorporating GPP is about 60% at 800 C. K E Y W O R D Scompressive strength, elevated temperature, ground pumice powder, steel fiber reinforced selfcompacting concrete, UPV
Bu çalışmanın amacı; manyetize edilmiş suyun, lifli ve lifsiz reaktif pudra betonların (RPB) basınç ve eğilme dayanımı üzerindeki etkisini incelemektir. Farklı manyetik alan şiddetleri manyetik su üretimi için kullanılabilmektedir. Bu çalışmada; 0.8-1 ve 1.2 Tesla şiddetindeki üç farklı manyetik alan şiddeti seçilmiştir. Manyetik su üretimi için farklı manyetik alan şiddetlerinde bekletme süresi 20 dakika olarak sabit alınmıştır. Elde edilen sonuçlar incelendiğinde; normal su kullanımı yerine manyetik su kullanımı, 7 ve 28 günlük basınç ve eğilme dayanımlarının artmasını sağladığı görülmüştür. Ayrıca manyetize edilmiş suyun, RPB'lerin basınç ve eğilme dayanımına olumlu etkisi olduğu ve dayanımı artırmak için en verimli manyetik alan şiddetinin 1 Tesla olduğu tespit edilmiştir.
Condition deterioration of the concrete, especially in corrosive environments, is one of the most common imperfection and disadvantages of reinforced concrete structures. Sulfates' main damages are expansion and loss of strength. Geopolymers are one of the newest structural materials that have been widely developed in recent years for use in sustainable designs. Geopolymers are environmentally friendly and considered as green materials since they are effective in sustainable and eco‐friendly material design concept. One of the most important matters in the sustainability of structural materials is their resistance against sulfates. So far, the durability of perlite‐based geopolymers against sulfates and acids has not been investigated. In this research, the fineness influence, curing conditions, duration of maintaining in the sulfate environment at different weight percentage in solution (i.e., 2.5, 5, 7.5, and 10%) have been investigated. Compressive strength and microstructure changes of geopolymer samples have been assessed in this research. As a result, optimum increase in perlite fineness causes increase in compressive strength and durability of samples against sulfate attack. Also, samples that have been cured by autoclave method have better mechanical properties and better durability. It is hoped that by filling these deficiencies and gaps, a positive step can be taken to accelerate attempts for finding a suitable replacement for ordinary Portland cement.
As a striking contribution of metakaolin to geopolymer concretes, the varying contents of metakaolin with quartz powder are included the mixtures with ground granulated blast furnace slag, and quartz sand to observe the mechanical, physical, transport, microstructure, and nuclear protection parameters of the samples, within this study. The geopolymer concrete samples are tested for the mechanical transport and physical properties depending on the curing time, curing temperature, and the raw/by‐product material type. The results show that the samples containing the most metakaolin performed well with a 24‐h compressive strength of 131.78 MPa. Increasing the curing temperature and curing time affected both mechanical, physical and transport properties. In addition, the microstructure of the samples was analyzed by scanning electron microscopy, x‐ray diffraction, and Fourier transform infrared spectroscopy. Moreover, the effect of increasing metakaolin reinforcement on the nuclear protection capacity of the produced geopolymer concretes with experimental gamma transmission and neutron dose measurements was investigated. The M3 sample with high content of both metakaolin and granulated blast‐furnace slag showed the highest resistance to gamma photons in the energy range of 0.081–0.383 MeV. The produced geopolymer samples absorbed almost 40% of the fast neutrons with 4.5 MeV energy. Neutron removal cross sections of the produced geopolymer concretes are in the range of 0.0952–0.0949 cm−1 and are larger than those of B4C, graphite, and boric acid. The findings of this study revealed that the addition of metakaolin improved the mechanical, nuclear shielding and structural properties of geopolymer concretes.
Considering global trends in sustainable and green development as well as the major drawbacks of conventional hydraulic cement, accelerate attempt for finding a suitable alternative and likely cause further development of geopolymeric cements in future. Influences of Nano scale Materials in improving the mechanical properties of ordinary Portland cement have been obviously proved. Despite the widespread use of these materials in different fields of science, for instance, chemicals engineering, materials engineering and even ordinary Portland cement, the effect of Nano scale materials in geopolymers has not been investigated deservedly. The purpose of this study is creating bridges to mitigate these gaps and shortcomings. Very fine silica particles (micro and Nano-silica) effects in ferrochrome slag based geopolymer have been evaluated in this research. Elazığ ferrochrome slag was used as the main aluminosilicate source and then it was blended with Nano silica or silica fume in little amounts in order to accelerate geopolymerization. Nano-silica and silica fume have been used at 2,4,6,8 and 10% of total binder weight in this study due to probe fine silica effect on the mechanical specification of produced material such as compressive strength, Static modulus of elasticity, Tensile Strength and microstructural change. The experimental results show all of these mention mechanical properties have been improved with adding fine silica in geopolymer mixes in optimum percentage of total binder weight. The best percentage of fine silica partial replacement instead of FS is 6% at all of silica fume and three Nano particle size (15, 30 and 45 nm). SEM images assessment demonstrated homogenous and denser texture with acceptable chemical bonds improvements for samples with optimum Nano-silica dosage. Compressive strength increase can be explained by densification of the matrix texture by using of Nano-silica and silica fume at optimum dosage.
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