The research aims to determine the best combination of the controlling factors that govern geopolymer concrete’s mechanical and physical properties by utilizing industrial waste. Therefore, a review on the controlling factors was conducted. Firstly, it is to identify the controlling factors, namely chemical composition, alkali activation solution, water content, and curing condition. Secondly, understanding the relationship between these controlling factors and the properties of geopolymer concrete. These factors are analysed to the mix proportion components. Finally, a new proportion method is proposed based on combining ACI 211 standard and recommended molar ratios of oxides involved in geopolymer synthesis. The effect of aggregate has been taken into account by applying the absolute volume method in mix design. Based on the results of the study, it is expected to determine the optimal mix proportions based on multi-responses.
Concrete is a composite material that mainly consists of mineral aggregates bound by matrix of hardened cement paste. Composition and microstructure of hardened cement paste have important influences on the properties of concrete exposed to high temperatures. An extensive experimental study was carried out to analyze the postheating characteristics of concretes subjected to temperatures up to 800 °C. Major parameters of our study were the slag content of cement (0, 16, 25, 41 or 66 m%) and the value of maximum annealing temperature.Our results indicated that (i) the number and size of surface cracks as well as compressive strength decreased by the increasing slag content of cements due to elevated temperature; (ii) the most intensive surface cracking was observed by using Portland cement without addition of slag.The increasing slag content of cement increased relative post-heating compressive strength. Tendencies of surface cracking and reduction of compressive strength were in agreement, i.e. the more surface cracks, the more strength reduction.
Our study was directed to analyse the influence of various types of cements on the behaviour of concrete at high temperatures. In our experiments binary blended and ordinary Portland cements were involved: two Portland cements with different clinker compositions and Portland cements containing trass or fly ash additives as replacement of clinkers. In the first part of the study we focused on the influence of cement types where various cement paste specimens were investigated. Then, based on the results, concretes prepared with some selected type of cements were also studied. Our studies have proved that the pozzolanic additives and their increased amount have a favourable effect on the heat resistance (fire resistance) properties of concrete.
Abstractin the hardened cement paste -through pozzolanic reactions -additional hydration products can be formed by the use of supplementary cementing materials (scms). the expected results of these processes are: increase in strength, decrease in permeability and the improvement of other important durability properties. in the present research, properties of mortar mixtures were investigated with different cement substitution rates of scms both in fresh and hardened conditions. the consistence of mixtures was determined by flow table test, and the change in workability was repeatedly measured until 120 minutes. the specimens were stored in water up to the age of 7 days then under laboratory conditions (in climate chamber of 20±3°c temperature and rH=65% relative humidity) up to the age of 28 days. Afterwards half of the specimens were immersed into and stored under water and the other half was kept continuously under laboratory conditions. the properties of the hardened specimens (flexural tensile strength, compressive strength, water absorption, apparent density and apparent porosity) were investigated at the age of 28, 56, 90 days. seven mortar mixtures were made of cem i 42.5 n Portland cement with different cement substitution ratios of metakaolin (mk) and/or silica fume (sF). Quartz sand was used as aggregate with the range of 0/2 mm particle size. the results of consistence measurements showed that the flow values of the fresh mortar mixtures which contain scms are smaller comparing with the reference mixtures (without scms), since the physical properties of these materials (particle size, specific surface area, particle shape, etc.) influence the consistence. the specimens with smaller substitution ratio showed more effective utilization of scms in the view of strength. the water absorption and apparent porosity were higher, and at the same time the apparent density was smaller than those of the mixtures with higher substitution ratios.
Abstract. Nowadays the most suitable and widely used construction material is concrete. We could develop concrete for every request in connection with the properties of fresh concrete and the quality of hardened concrete, too. The demand is rising in application of special concretes, like high performance and ultra high performance concretes (HPC, UHPC). These are usable in extreme natural circumstances or in very corrosive surroundings (for example: sewage farm, sewer, cooling tower, biogas factories). The pH value of the commercial sewage is between 7-8, but this value is often around 4 or less. The concrete pipes, which transport the sewage, are under corrosion, because above the liquid level sulphuric acid occurs due to microbes. Acidic surroundings could start the corrosion of concrete. When the pH value reduces, the influence of the acids will increase. The most significant influence has the sulphuric acid. The pH value of sulphuric acid is about 1, or less. Earlier in the cooling towers of coal thermal power stations used special coating on the concrete wall. Recently application of high performance concrete without polymeric coating is more general. Cementitious supplementary materials are widely used to protect the concrete from these corrosive surroundings. Usually used cementitious supplementary materials are ground granulated blastfurnace slag (GGBS), flying ash (FA) or silica fume (SF). In the last years there has been a growing interest in the application of metakaolin. Metakaolin is made by heat treatment, calcinations of a natural clay mineral, kaolinite. In our present research the chemical resistance of mortars in different corrosive surroundings (pH=1 sulphuric acid; pH=3 acetic acid) and the chloride ion migration were studied on series of mortar samples using rapid chloride migration test. Cement paste and mortar samples were made with 17% metakaolin replacement or without metakaolin. The following cements were used: CEM II/A-S 42.5 N, CEM I 42.5 N-S. We concluded that the replacement of cement by metakaolin results in significant increases in compressive and tensile strengths and it prevents the infiltration of harmful substances.
When it comes to flood protection, the established method is to
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