Experimental Study on Self Compacting Fibrous Concrete Comprising Magnesium Sulphate Solution Treated Recycled Aggregates

It appears that the awareness and intentions to use recycled concrete aggregate (RCA) in concrete are expanding over the globe. The production of self-compacting concrete (SCC) using RCA is an emerging field in the construction sector. However, the highly porous and absorptive nature of adhered mortar on RCA’s surface leads to reduced concrete strength, which can be removed with the application of various techniques, such as acid treatment. This study investigated the effect of the partial replacement of silica fume by cement and natural aggregate (NA) by RCA with and without steel fibre. The used RCA was treated with magnesium sulphate solution. It was immersed in solutions with different concentrations of 10%, 15% and 20% and for different periods of 5, 10 and 15 days. Sixteen mixes were prepared, which were divided into six groups with or without 1% of steel fibre content. The fresh properties, compressive strength, split tensile strength and impact resistance were examined. The results revealed that the strengths of the mixes with 20% RCA were marginally better than those of the control mixes. The compressive strength and split tensile strength were reduced by 34% and 35% at 60% RCA content, respectively, as compared to the control mixes.

Electrodialysis of a sodium sulphate solution with experimental bentonite-modified bipolar membranes

The aim of this work is to study the characteristics of the electrodialysis of a sodium sulphate solution with experimental bipolar membranes based on the MA-41 anion exchange membrane and a liquid sulphonated cation-exchanger modified with bentonite clays. The conversion of sodium sulphate was conducted by electrodialysis with bipolar membranes obtained by applying a liquid sulphonated cation-exchanger containing particles of bentonite clay to the MA-41 anion-exchange membrane.To increase the performance of membranes in terms of hydrogen and hydroxyl ions, we carried out organomodifications of bentonite with alkyldimethylbenzylammonium chloride and stearic acid at various concentrations. The bipolar membrane with the addition of bentonite modified with alkyldimethylbenzylammonium chloride (2 wt%) showed a higher performance in terms of H+-ions. The bipolar membrane with bentonite modified with stearic acid (3 wt%) added to its cation-exchangelayer is the most effective in terms of obtaining a flux of OH--ions. It was shown that a combination ofalkyldimethylbenzylammonium chloride (2 wt%) and stearic acid (3 wt%) used to modify bentonite can increase the performance of the bipolar membrane during the conversion of sodium sulphate, both in terms of the acid and alkali.

Possibilities of Using Pumice Aggregates into Thermal Insulation Lining of Industrial Chimneys

This paper deals with the possibility of using pumice aggregates into thermal insulation lining of industrial chimneys. It introduces the construction of modern chimneys and mentions possible risks and degradation processes associated with condensate penetration. In the experiment, mixtures with pumice as aggregate were prepared. The thermal insulation properties, compressive strengths and the resistance to sulphates in a 5% sodium sulphate solution were evaluated and compared.

Monitoring of Chemical Resistance of New Grouting Materials

This paper deals with the study of chemical resistance of new cement-based grout for invert grouting. The aim of this work is to verify new mixtures with specific admixtures. The study monitors resistance to external sulphate attack. Specimens were placed into sulphate solution 29.8 g∙l-1 (44 g∙l-1 Na2SO4) according to DIN19753 standard. Based on the results gained, new mixtures will be designed and optimized by addition of suitable secondary raw materials (fly ash, waste foundry sand, waste glass, waste filers).

Possibilities of Using Pumice Concrete as Thermal Insulation Lining of Industrial Chimneys

This paper deals with the possibility of using pumice concrete as thermal insulation lining of industrial chimneys. Two formulas were prepared, the first from sulphate resistant cement and the second as a reference mixture from Cem I 42.5R. The thermal insulating properties of the prepared recipes will be evaluated as well as the resistance to the action of sulphates in 5 % sodium sulphate solution. No significant decrease in strength was observed when samples were stored in 5% sodium sulfate solution for 60 days. Only the reference series reported a significant unexpected decrease in strength.