Sulphide oxidation mortar tests for evaluation of the oxidation potential of sulphide-bearing aggregate

This paper proposes two new sulphide mortar bar tests. The two tests involve two exposure conditions: the first one relies on soaking the sample in an oxidizing agent (6% sodium hypochlorite) for three hours at room temperature to promote oxidation while the other test adopts a range of temperatures and relative humidity that promote oxidation and sulphate attack. Both tests were effective in discriminating between aggregates with oxidizable sulphide and those without. Moreover, the use of low-calcium fly ash at 25% and slag at 30% reduced the expansion but not to the level of samples with non-sulphide aggregates. On the contrary, 10% of metakaolin produced more expansion.<br>

Sulphide oxidation mortar tests for evaluation of the oxidation potential of sulphide-bearing aggregate

This paper proposes two new sulphide mortar bar tests. The two tests involve two exposure conditions: the first one relies on soaking the sample in an oxidizing agent (6% sodium hypochlorite) for three hours at room temperature to promote oxidation while the other test adopts a range of temperatures and relative humidity that promote oxidation and sulphate attack. Both tests were effective in discriminating between aggregates with oxidizable sulphide and those without. Moreover, the use of low-calcium fly ash at 25% and slag at 30% reduced the expansion but not to the level of samples with non-sulphide aggregates. On the contrary, 10% of metakaolin produced more expansion.<br>

Sulphide oxidation mortar tests for evaluation of the oxidation potential of sulphide-bearing aggregate

This paper proposes two new sulphide mortar bar tests. The two tests involve two exposure conditions: the first one relies on soaking the sample in an oxidizing agent (6% sodium hypochlorite) for three hours at room temperature to promote oxidation while the other test adopts a range of temperatures and relative humidity that promote oxidation and sulphate attack. Both tests were effective in discriminating between aggregates with oxidizable sulphide and those without. Moreover, the use of low-calcium fly ash at 25% and slag at 30% reduced the expansion but not to the level of samples with non-sulphide aggregates. On the contrary, 10% of metakaolin produced more expansion.<br>

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).

Impact Resistance and Sodium Sulphate Attack Testing of Concrete Incorporating Mixed Types of Recycled Plastic Waste

Impact resistance, water transport properties and sodium sulphate attack are important criteria to determine the performance of concrete incorporating mixed types of recycled plastic waste. Nine mixes were designed with different combinations of the three plastic types; Polyethylene terephthalate (PET), High density polyethylene (HDPE) and Polypropylene (PP). The plastic partially substituted the coarse aggregate (by volume) at various replacement ratios; 10%, 15%, 20% and 30%. The impact resistance and water transport properties were evaluated for nine mixes while sodium sulphate attack test was performed for three mixes. The results showed that the addition of mixed recycled plastic in concrete improved the impact resistance. The highest impact resistance improvement was achieved by R8 (PET + HDPE + PP) at 30% replacement which was 4.5 times better than the control mix. Water absorption results indicated a slight increase in all plastic mixes while contradictory results were observed for sorptivity test. Analysis of sodium sulphate attack results showed that incorporating 30% mixed plastic reduced the sodium sulphate resistance slightly due to the collective effect of plastic entrapping of sulphate ions after 80 cycles. This study has shown some positive results relating to the impact performance of Mixed Recycled Plastic Concrete (MRPC) which enhances its use in a sustainable way.

Physical-Mechanical Properties of Cupola Slag Cement Paste

The high consumption of natural resources in the industrial sector makes it necessary to implement measures that enable the reuse of the waste generated, seeking to achieve circular economy. This work assesses the viability of an alternative to the use of CEM III B 32.5 R cement in mortars for the internal coating of centrifugally spun cast iron pipes for water piping. The proposal is to reuse the slag generated in the casting process after being finely ground, as an addition mixed with CEM I 52.5 R cement, which is basically Portland clinker. In order to analyse this possibility, an extensive experimental campaign was carried out, including the analysis of the cupola slag (micro-structural and chemical composition, leachates, setting time, vitrification, puzzolanicity and resistance to sulphate) and regarding the mortars (workability and mechanical properties). The experimental programme has shown that the optimum substitution is achieved with a replacement percentage of 20% of the cement, with which similar workability, superior mechanical properties and guaranteed resistance to sulphate attack are obtained. In addition, both economic and environmental savings are achieved by not having to transport or landfill the waste. In addition, the new cement is cheaper than the cement currently used.

Effect of Ultrafine Metakaolin on the Properties of Mortar and Concrete

This study investigated the influence of ultrafine metakaolin replacing cement as a cementitious material on the properties of concrete and mortar. Two substitution levels of ultrafine metakaolin (9% and 15% by mass) were chosen. The reference samples were plain cement concrete sample and silica fume concrete sample with the same metakaolin substitution rates and superplasticizer contents. The results indicate that simultaneously adding ultrafine metakaolin and a certain amount of polycarboxylate superplasticizer can effectively ensure the workability of concrete. Additionally, the effect of adding ultrafine metakaolin on the workability is better than that of adding silica fume. Adding ultrafine metakaolin or silica fume can effectively increase the compressive strength, splitting tensile strength, resistance to chloride ion penetration and freeze–thaw properties of concrete due to improved pore structure. The sulphate attack resistance of mortar can be improved more obviously by simultaneously adding ultrafine metakaolin and prolonging the initial moisture curing time.

Role of supplementary cementing materials on reducing damage due to internal sulphate attack in concrete

The effect of supplementary cementing materials (SCM) on internal sulphate attack in mortars was evaluated. Different types and levels of SCM were investigated where a mixture of hemihydrate and calcium carbonate fillers were used in the mixtures as a source of sulphate and carbonate, respectively. In addition, mixtures containing aggregates with high sulphate content were also examined to understand the role of sulphate from aggregate on the expansion. It has been found that the internal sulphate attack can be reduced through the use of SCM with high reactive alumina such as Metakaolin. It was hypothesised that the beneficial effect of Metakaolin lies in its ability to reduce ion mobility within the matrix, and perhaps raise the alumina/sulphur in the system favoring the formation of non-expansive monosulphoaluminate. However, at high levels of sulphate, none of the SCM provided successful protection against internal sulphate attack.