Effect of Silica Fume as a Component of Alternative Binder on the Selected Technically Important Characteristics of Bio-Aggregate-Based Composites

This experimental study was focused on the application of an alternative binder based on MgO, and the variation of its components by the combination of two MgO products obtained by the calcinations of natural magnesite, siliceous materials (river sand and silica fume), and alkaline admixture in the mixture for a preparation of composite based on biomass waste such as hemp hurds as organic filler. This paper presents the results of the effect of an MgO binder composition on the compressive strength of the bio-aggregate-based composites. Other physical properties, such as the bulk density, thermal conductivity coefficient, and water absorption, were also investigated. The measured strength parameters of the bio-composite samples that were hardened for 28 days demonstrate that the binder consisting of optimal calcined MgO and silica fume as a total replacement for sand ensures a good binding of the matrix with hemp hurd compared to other varied compositions of alternative binder. No significant differences in bulk density and thermal conductivity values were found for these composites. However, the bio-composite specimen with an MgO⁻SiO2 matrix had the highest compressive strength and achieved the lowest value of water absorption. An increase in hardening time of up to 90 days led to a significant improvement of strength as well as reduction in permeability

Frost resistance of cement composites prepared on the basis of waste water from a concrete plant

This article presents the results of a research dealing with the use of waste water from concrete industry as a possible substitution of mixing water during the production of cement composites. This experimental research involved the preparation of two recipes of cement composites, named R1 and R3. Mixing water in these recipes was replaced with waste water from a concrete plant in the amount of 25, 50, 75 and 100%. Samples of recycled waste water, which were tested for the content of sulphates, chlorides and alkali according to ČSN EN 1008, were taken in order to determine the properties of waste water from a concrete plant. The prepared test specimens were tested for frost resistance after 100 freezing cycles according to ČSN 73 1322. The results of the frost resistance test showed that the required value of the frost resistance coefficient of 0.75 according to ČSN 73 1322 was achieved only in case of recipe R1 based on Portland cement CEM I 52.5R and 75 and 100% substitution of the mixing water with recycled water from a concrete plant

Characterization of cement composites based on recycled cellulosic waste paper fibres

Nowadays, there is paying an attention to the utilization of natural, renewable and biodegradable resources of raw materials of lignocellulosic character, residues from agricultural crops and wood processing as well as waste from papermaking industry in building composite materials preparing. Also recycled fibres coming from waste paper are considered as valuable material. The objective of this study is to utilize these recycled cellulosic fibres into cement composites and characterise their impact on resulting physical and mechanical properties of fresh and hardened cement composites. Manufactured cement composites contained 0.2%, 0.3% and 0.5% addition of cellulosic fibres. In fresh fibre cement mixtures reduction in workability with increasing amount of cellulose fibres was noticed. Density as well as compressive and flexural strength of 28 and 90 days hardened fibre cement composites was tested. Distribution of cellulosic fibres with 0.5% addition in hardened fibre cement composites was also observed. The results of density determination of 28 and 90 days hardened fibre cement composites showed reduction in their values related to weight lighter concretes. Compressive strengths of fibre cement composites have shown decreasing character with increasing added amount of cellulosic fibres into the mixture up to 0.5%. Maximal decrease in compressive strength values was observed in composites containing 0.5% of cellulosic fibres. However, obtained strength parameter values of hardened composites had satisfying results for their application in construction as non-load bearing building material