Advances in Science and Technology Vol. 145

Abstract: An experimental study was conducted to investigate the mechanical properties of fly ash geopolymer binder system containing 0% to 30% ferrochrome slag. Paste and mortar samples were prepared using a mixture of sodium silicate (SS) and sodium hydroxide (SH), as the alkali – activator solution made at varied SS/SH ratio of 1.5 to 2.3, along with varied sodium hydroxide concentration ranging from 10.7 to 15.2 M. The ratio of alkali – activator to raw aluminosilicate material, was kept constant at 0.50, 0.52 or 0.54. Paste or mortar cubes of 50 mm size were cast and cured at 23, 40, 60 or 80 °C for compressive strength testing, while prisms of 25 × 25 × 285 mm size were prepared for drying shrinkage monitoring. Also measured were workability, density, water absorption and pore volume. Microanalytical studies were done using scanning electron microscopy, X – ray diffraction analysis, and Fourier transform infrared spectroscopy. It was found that fly ash geopolymer mortars containing 10% ferrochrome slag and cured at normal temperature gave the optimal compressive strength. There was significant increase in drying shrinkage of mortars, as the content of ferrochrome slag increased, but overall values were within normal range. Keywords: Fly ash geopolymer, Compressive strength, Ferrochrome slag, Drying shrinkage.

Abstract: This paper presents the results of an experimental determination of the coefficient of thermal expansion of hardened alkali-activated slag pastes. In the experiment, three different activators were used – liquid sodium silicate, sodium carbonate and sodium hydroxide. The slag volume fraction for all paste types was set to 0.52. The specimens’ internal moisture content and shrinkage strains were plateaued at ambient laboratory conditions (temperature = 22 ± 2 °C, relative humidity = 55 ± 5 %) at the testing time. All of the specimens were wrapped into the polyethylene foil before the start of thermal dilation measurements and stored in the Q-Cell incubator in which they were subjected to temperature cycling from 5 °C to 30 °C. Length changes caused by the temperature changes were measured with dilatometers supplemented by continuous strain gauges measurement. The results show different values of the coefficient of thermal expansion depending on the activator type. Moreover, the strains recorded by the dilatometer through the steel pins embedded into the ends of specimens and by the strain gauges placed in the core of the test specimens led to different resulting values of the coefficient of thermal expansion.

Abstract: In this paper, more than 20 mixtures of metakaolin/blast furnace slag alkali-activated mortar mixtures with a maximum grain size of 2.5 mm are investigated. Parameters varied include mixing procedure, curing conditions of which the most used procedure is sealed curing at 70°C for 7 days, granular skeleton, water-to-solid ratio (0.35 to 0.60), metakaolin content (30 to 100%), and type of alkaline activator (sodium silicate solution or potassium silicate solution). The mix design is based on chemical calculations based on the oxide composition of the precursors and activators. Fresh material properties i.e. initial and final setting time, and workability are measured for part of the mixtures. Mechanical tests have been performed on mortar size prisms in order to determine the compressive and flexural tensile strength of all mixtures. The range of compressive strength varies in between 50 and 142 MPa. Based on the results Feret’s law seems to be valid for alkali-activated materials as well.

Abstract: Portland cement has been replaced with 50% ground, granulated blastfurnace slag (ggbs) of two types. The influence of 2 and 4% calcium nitrate accelerator on early hydration of such binders was investigated by isothermal calorimetry as well as X-ray diffraction and thermogravimetry. The strength development of mortar based on these binder blends has been followed up to 28 days and the influence of calcium nitrate discussed. One ggbs lower in SiO₂, A_l2O₃ and MgO yielded somewhat lower strength (about 90%) than the other. Addition of calcium nitrate led to lower strength at 1 day, but higher strength from 3 days on-wards. The blends with the two ggbs achieved similar strength at 7 and 28 days when blended with 4% calcium nitrate. Calcium nitrate led to more ettringite formation and AF_m phases (probably nitrate version) at 1-day sealed curing. However, the calcium hydroxide content was reduced. Potential explanations for calcium hydroxide reduction are discussed.

Abstract: Pervious concrete is considered an advanced pavement material in terms of environmental benefits resulting from its basic feature - high water permeability. While natural aggregate is a standard component for permeable concrete production, the paper presents the potential of air-cooled blast furnace slag aggregate. The aggregate is specific for its open internal structure and at the same time high hardness and strength, which was assumed to be advantageous for this type of concrete. As permeable concrete is characterized by a specific structure and low amount of binder, it needs for optimization of kind and composition of aggregate, as well as the quantity and quality of the binder. In the experiment, following variables of composition were applied: a ratio of binder to aggregate b/a (0.28 and 0.36), a ratio of fine to coarse aggregate f/c (0.1, 0.2 and 0.3), and a set of blended cements. Experimental results point to the specific benefit of slag aggregate for permeable concrete production. The values of total porosity (30-38%) and permeability (4.6-17.5 mm/s) are higher than those recommended by most publications, as well as than those of concretes with natural aggregates. The compressive strength runs from 7.5 MPa to 15.0 MPa depending on the variables, while the effect of fine aggregate portion on both compressive strength and hydraulic conductivity is found to be much greater than that of the amount of binder. An important aspect is that, due to the nature of the aggregate, sufficient permeability is maintained even with higher proportion of fines. The range and variance values of the individual properties indicate that a change in the quality of the binder causes less variation in the results than a change in the composition of the mixtures.

Abstract: Concrete mixtures with water-to-cement ratios (w/c) of 0.50, 0.40, and 0.30 were prepared. In the last mixture, 10% and 20% of aggregates were substituted with water-saturated expanded clay. This resulted in the creation of self-cured concrete mixtures. The mechanical properties and frost resistance of these mixtures were discussed concerning the results obtained for concrete without aggregate substitution. It was observed that self-curing can enhance the frost resistance of HPC, even though LWA reduces both flexural and compressive strength.

Abstract: The subject of the study presented in this paper is to quantify the effect of fiber content on the mechanical and mainly fatigue response of fine-grained cement-based composites. The reference cement-based composite was without fibers. Three types of fibers were used as dispersed reinforcement: tire cords (waste material), steel, and polypropylene. For each type of fiber, mixtures with varying reinforcement levels per volume were prepared: 0.0 % (reference composite), 0.5 %, 1.0 %, and 1.5 %. Prismatic specimens 40 mm × 40 mm × 160 mm were prepared and tested. A total of 10 composite variants were investigated. The ages of the specimens for the static three-point bending tests were 28 days, for the compression tests were 28, 120, and 275 days. While for the fatigue tests, it was approximately between 110 and 180 days. The obtained compressive strength values for the above-mentioned composite ages were approximated by a selected exponential function and the results of the fatigue tests were standardized to a nominal age of 28 days using them. All used types of reinforcement increase the strength values of the composites even from the lowest fiber doses. A positive effect of fiber dosage above 0.5 % on the fatigue behavior of composites was shown only in the case of reinforcement with commercial steel fibers.

Abstract: The elastic modulus (E_c) of concrete is usually calculated from the compressive strength (f_c) in the design of concrete structures using standard models found in the various design codes. Most of these models were fundamentally developed for concrete made with natural coarse aggregate (NCA). Concrete containing coarse recycled concrete aggregate (CRCA) is known to have inferior mechanical properties to concrete made with NCA. Accordingly, the E_c-f_c relationship of CRCA concrete differs from that of NCA concrete. Hence, a number of researchers have endeavoured to develop predictive models for concrete made with CRCAs using different software programs. In an attempt to contribute to this subject, the present study seeks to propose a new model for predicting the E_c of CRCA concrete using an empirical approach. Data obtained from the literature was used to develop the model. Validations of the model using independent data sources gave realistic predictions. The new model can be used for practical E_c prediction, design, and analysis of sustainable concrete structures made with CRCAs.

Abstract: DARE2C (Durable Aluminium Reinforced Environmentally-friendly Concrete Construction) project is to develop a more environmental-friendly concrete and use aluminium (Al) as reinforcement material, instead of steel. The new concrete uses supplementary cementitious materials (SCM), which provides a low alkaline environment suitable for aluminium reinforcement. Unlike steel, aluminium has a better stability in medium pH environment, which can largely improve the durability of the new Al-reinforced concrete (RC). Cover thickness can be reduced since aluminium withstands environment and carbonation does not pose a threat. The usage of lighter aluminium as reinforcement would help greatly reduce the total weight of the Al-RC structure. The objective of this work is to investigate the compatibility of different aluminium alloys in the new DARE2C concrete by gas chromatography measurement during the cement hydration. Together with the pull-out test results, the best aluminium candidate will be determined.DARE2C (Durable Aluminium Reinforced Environmentally-friendly Concrete Construction) project is to develop a more environmental-friendly concrete and use aluminium (Al) as reinforcement material, instead of steel. The new concrete uses supplementary cementitious materials (SCM), which provides a low alkaline environment suitable for aluminium reinforcement. Unlike steel, aluminium has a better stability in medium pH environment, which can largely improve the durability of the new Al-reinforced concrete (RC). Cover thickness can be reduced since aluminium withstands environment and carbonation does not pose a threat. The usage of lighter aluminium as reinforcement would help greatly reduce the total weight of the Al-RC structure. The objective of this work is to investigate the compatibility of different aluminium alloys in the new DARE2C concrete by gas chromatography measurement during the cement hydration. Together with the pull-out test results, the best aluminium candidate will be determined.