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.

The influence of the addition of cigarette butts, as dangerous waste material, to the properties of the brick clay "Čavka" near Busovača was studied. The cigarette butts were added to the clay in amounts of 5 mass% and 10 mass%. Testing of the samples included testing of consistency, plasticity, Atterberg plastic and liquid limits, drying and firing behavior and refractoriness. Also, apparent density, apparent porosity, water absorption, flexural and compressive strength were investigated on the samples fired at different temperatures. Thermal conductivity was tested on sample fired at 1173 K. Addition of cigarette butts improved insulation characteristics and drying sensitivity, while other properties remain within the required limits for brick industry. Copyright © 2019 International Energy and Environment Foundation All rights reserved.

This paper presents the effect of nanosilica on the early strength of cement mortars. Three series of samples were investigated: one with ordinary Portland cement CEM I 52,5 N and two with siliceous and calcareous fly ashes as a partial cement replacement (25 wt. %). The results reveal that by using small amount of nanosilica (2 and 4 wt. % of binder) water demand of all tested cement pastes increases proportionally to nanosilica content, while the setting time is not significantly influenced. Compared to the reference samples, the addition of 2 % nanosilica increased two-days strengths, while addition of 4 % nanosilica reduced two-days strengths of the mortar samples.

The paper examined the conventional vibrating castables composed of a mixture of high alumina cement and chamotte waste with addition of fly ash and clay. The influence of particle size distribution on density, porosity, water absorption, cold crushing and flexural strength of castables was investigated. Particle size distribution was determined by the Dinger and Funk equation, using four different coefficients q. Three series of samples were investigated. In the first series as the smallest fraction was used high alumina cement only and chamotte waste in other fractions. In the second and third series the amount of cement was 20.6 % for all mixtures with different coefficient q. Instead part of cement and instead the finest fraction of chammotte waste it was used fly ash in second and clay in third series. Fly ash and clay do not significantly change the properties of castables and can be used as replacment for part of cement and for finest fraction of chamotte waste.

In this paper are investigated microstructural, phase, physical and mechanical properties of mullite ceramics obtained from clay and Bayer electrofilter fines. Clay and alumina were mixed in such ratio that provides the amount of Al2O3 and SiO2 corresponding composition of mullite. One mixture was manually mixed and other was milled three hours in ceramic mill. After isostatic molding and heat treating at 1580°C and 1635°C XRD analysis revealed approximately 60% of mullite and 40% of corundum in first mixture and in second mixture 70% of mullite and 30% of corundum. Two types of mullite were observed in SEM micrographs beside corundum grains and glassy phase. The results of investigation indicate that preparation of mullite ceramics from these raw materials is possible, if clay and alumina are well homogenized and milled before molding.

The increase of sustainability importance in the world has led to a greater concern of the environmental impact of using concrete in construction. Self-cleaning concrete is attractive not only because of its self-cleaning abilities but also because of its environmentally friendliness. The use of this contemporary cement composite in urban and interurban areas can reduce maintenance cost and ensure a cleaner environment. This paper provides a review on self-cleaning concrete, the main principle behind self-cleaning concrete and its application nowadays.