Properties of concrete containing the ground calcined low-kaolinite clay was experimentally studied. Clay, calcined at 900 and 1000°C, was used as a partial replacement of cement at dosage of 20 % by the weight of cement. Tests performed on concrete samples include the consistency, air content, compressive strength and flexural strength. The experimental results show a moderate decrease in slump, as well as in compressive and flexural strength comparing to concrete containing only cement CEM I as a binder. Better results were obtained with concrete containing clay calcined at 1000°C. Further research is needed to determine the optimal dosage of calcined clay in concrete, as well as the optimal temperature of clay calcination.

This paper presents the results of an experimental investigation into the effect of nano-silica addition on the mechanical properties and durability of concrete. Three mixes of concrete containing 0%, 2%, and 4% nano-silica by weight of cement were tested. The slump of fresh concrete as well as compressive strength, dynamic modulus of elasticity at 2, 7, 28, 90, and 180 days, and flexural strength at 2, 28, and 90 days of hardened concrete were determined. As for indicators of concrete durability, the total volume of permeable voids, water absorption, the rate of water absorption, and the freeze-thaw scaling resistance were determined. Test results showed that the incorporation of nano-silica in concrete resulted in an improvement of all mechanical properties of concrete, as well as concrete durability parameters that are tested.

Fly ash class F from Thermal Power Plant “Stanari” was used in combination with highly plastic brick clay from Busovača to develop building bricks. The brick clay and fly ash were characterized for chemical and mineralogical composition, grain size distribution, and specific gravity. The fly ash has a higher proportion of larger particles and lower specific gravity than clay. The brick clay was mixed with 20, 40, and 60 wt. % of fly ash, formed in a prismatic shape, dried and then fired at 800, 900, and 1000 °C. The fired prisms were characterized for water absorption, apparent porosity, apparent density, and strength and compared with conventional clay prisms. The addition of fly ash of 20, 40, and 60% reduced the mass of the samples by 14, 23, and 31%, increased apparent porosity by 60, 100, and 160%, and reduced the compressive strength by 50, 80, and 90%, respectively. Conducted tests and comparative studies have shown that the fly ash “Stanari” can be used as an additive to the clay “Čavka” in the maximum amount of 20 % and the optimum firing temperature is 900 °C.

A method was proposed for the preparation of silica powders using sodium silicate as the silica source and carbon dioxide and hydrochloric acid as precipitating reagents. The effect of reaction temperature (20, 40, 60, and 80 °C) and SiO2 concentration in sodium silicate solutions (4, 6, 8, and 10 %) on silica morphology, dibutyl phthalate absorption, aggregate size distribution, and dispersion ability (agglomerates fragility) were investigated. The best properties of silica powder were achieved at reaction temperature 40 °C and SiO2 concentration 8 %. The properties of the silica sample obtained at optimal conditions were compared with properties of high-quality commercial silica used as rubber reinforcing filler. Also, the vulcanization characteristics and mechanical characteristics of rubber composites containing these two silica fillers were investigated. It was found that silica filler with excellent properties can be produced using the proposed method, while by tuning temperature and precursor concentration, the silica properties that are important for its reinforcing potential may be closely controlled.

The paper analyses the influence of cigarette butts and waste coffee grounds addition on the properties of the brick clay. The waste materials were added to the clay in amounts of 5 wt.% and 10 wt.%. Standard consistency, plasticity, drying and firing behaviour and refractoriness were tested on the clay sample and the samples with wastes additions. Apparent density, apparent porosity, water absorption, strength and thermal conductivity were investigated on the samples fired at 1173 K. Addition of the waste materials improved thermal insulation characteristics and drying shrinkage, while other properties remain within the required limits for brick industry.

<p style="text-align: justify;">In this paper, the possibility of proportioning self-compacting concrete with high volume calcareous fly ash (W) for precast elements has been investigated. So far, numerous mix design methods for self-compacting concrete have been developed, so as the most appropriate method in this investigation, the UCL method was chosen. In the first phase, the preliminary tests were conducted on the mortar mixtures using mini slump cone and mini V-funnel, and thereafter the optimal mixture composition was defined. In the second phase, self-compacting concrete mixture was prepared and tested. In the end, based<br />on the defined recipe, the precast elements were made and their properties were tested. On the basis of the examinations, it was found that it is possible to obtain high quality self-compacting concrete by using the relatively simple procedure according to the UCL method.</p>