Evaluation of the resistance of CAC and BFSC mortars to biodegradation : laboratory test approach

Biodeterioration of cementitious materials in sewer networks is a major concern for health and economic reasons. Essentially, it is due to the biological oxidation of H2S into H2SO4 leading to a local progressive dissolution of the cementitious matrix and the precipitation of expansive products likely to provoke cracks. However, it is widely known that CAC has a better performance in such environments but the mechanisms are not very well understood. Nevertheless, previous studies focused mainly on measuring the mass loss of the specimens accompanied with little information on the chemical alteration of the cementitious matrix. This study aims to compare the performance of CAC and BFSC mortars in sewer conditions using laboratory test (BAC-test). Leaching kinetics were evaluated by concentrations measurements of cementitious cations in the leached solutions and of sulphate production by the microorganisms. Moreover, SEM observations coupled with EDS analyses allowed the identification of the chemical alteration of the cementitious matrix

Laboratory test to evaluate the resistance of cementitious materials to biodeterioration in sewer network conditions

The biodeterioration of cementitious materials in sewer networks has become a major economic, ecological, and public health issue. Establishing a suitable standardized test is essential if sustainable construction materials are to be developed and qualified for sewerage environments. Since purely chemical tests are proven to not be representative of the actual deterioration phenomena in real sewer conditions, a biological test–named the Biogenic Acid Concrete (BAC) test–was developed at the University of Toulouse to reproduce the biological reactions involved in the process of concrete biodeterioration in sewers. The test consists in trickling a solution containing a safe reduced sulfur source onto the surface of cementitious substrates previously covered with a high diversity microbial consortium. In these conditions, a sulfur-oxidizing metabolism naturally develops in the biofilm and leads to the production of biogenic sulfuric acid on the surface of the material. The representativeness of the test in terms of deterioration mechanisms has been validated in previous studies. A wide range of cementitious materials have been exposed to the biodeterioration test during half a decade. On the basis of this large database and the expertise gained, the purpose of this paper is (i) to propose a simple and robust performance criterion for the test (standardized leached calcium as a function of sulfate produced by the biofilm), and (ii) to demonstrate the repeatability, reproducibility, and discriminability of the test method. In only a 3-month period, the test was able to highlight the differences in the performances of common cement-based materials (CEM I, CEM III, and CEM V) and special calcium aluminate cement (CAC) binders with different nature of aggregates (natural silica and synthetic calcium aluminate). The proposed performance indicator (relative standardized leached calcium) allowed the materials to be classified according to their resistance to biogenic acid attack in sewer conditions. The repeatability of the test was confirmed using three different specimens of the same material within the same experiment and the reproducibility of the results was demonstrated by standardizing the results using a reference material from 5 different test campaigns. Furthermore, developing post-testing processing and calculation methods constituted a first step toward a standardized test protocol

Metakaolin

peer reviewedMetakaolin (MK) is known to be a highly pozzolanic material that can be used in concrete. MK is usually produced by heating kaolin-containing clays, within the temperature range of about 600–900 ℃. This chapter summarizes the utilization of metakaolin in relevant worldwide standards, mainly in Europe and North America. The health, safety and environmental sustainability concerns on using metakaolin as a supplementary cementitious material are also addressed in this chapter. It is reported that MK incorporation has benefits on both early-age and long-term properties. On the other hand, this chapter also reports that the results of heat of hydration and rate of reaction in metakaolin-blended concrete are controversial and need further investigation. Overall, the optimum level of cement replacement by MK is around 10–20%, which provides concrete the maximum strength. Metakaolin appears to have an excellent potential as a supplementary cementitious material in structures made of high-performance concrete, because it controls deleterious expansion due to alkali-silica reaction in concrete (depending on the nature of the aggregate), and reduces the ingress of chloride by improving the microstructure and chloride binding behavior. © RILEM 2018

Report of RILEM TC 267-TRM phase 3: validation of the R3 reactivity test across a wide range of materials

RILEM TC 267 TRM– “Tests for Reactivity of Supplementary Cementitious Materials” recommends the Rapid Reliable Relevant (R3) test as a method for determining the chemical reactivity of supplementary cementitious materials (SCMs) in Portland cement blends. In this paper, the R3 test was applied to 52 materials from a wide range of conventional and alternative SCMs with the aim to validate such test. An excellent correlation was found between the cumulative heat release and the bound water determined following the R3 test method. Comparison of the R3 test results to mortar compressive strength development showed that all conventional SCMs (e.g. blast furnace slag and fly ashes) followed the same trend, with the notable exception of very reactive calcined kaolinitic clays. It is discussed, through an in-depth statistical regression analysis of the R3 reactivity test results and the 28 days relative compressive strengths, how reactivity threshold values for classification of the chemical reactivity of SCMs could be proposed based on the R3 test results

Report of RILEM TC 267-TRM phase 2: optimization and testing of the robustness of the R3 reactivity tests for supplementary cementitious materials

The results of phase 1 of an interlaboratory test, coordinated by the RILEM TC 267-TRM “Tests for Reactivity of Supplementary Cementitious Materials” showed that the R3 (rapid, relevant, reliable) test method, by measurement of heat release or bound water, provided the most reliable and relevant determination of the chemical reactivity of supplementary cementitious materials (SCMs), compared to other test methods. The phase 2 work, described in this paper aimed to improve the robustness of the test procedure and to develop precision statements for the consolidated test procedure. The effect of the pre-mixing and mixing conditions, and the impact of the mix design on the test method robustness were assessed and fixed for optimal conditions to carry out the R3 heat release test. The effect of the drying step was evaluated to define the R3 bound water test procedure in more detail. Finally, the robustness of the consolidated final test methods was determined by an interlaboratory study to define the precision statements

Synthesis of alite cement with low environmental impact by using sludge from a dam reservoir and zinc sulphate as a mineralizer

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Microstructural evolution of a sodium metakaolin-based geopolymer paste in neutral and CEM V basic environment

International audienceDuring their service life, geopolymers may be in contact with Portland cementitious materials. As their porosity is open and connected, resaturation by the cementitious pore solution is possible, and may lead to the material destabilization with durability issues. This paper investigates the evolution of a sodium geopolymer after immersion tests in a neutral and basic environment (deionized water, and CEM V pore solution) for 18 months. A chemical equilibrium takes place between the immersion solution and the geopolymer pore solution, leading to a decrease in alkalinity which may destabilize the geopolymer. A leaching of aluminum ions indicates a degradation of the geopolymer by a slow dissolution process. Apart from that, no major change in mineralogy or porosity was evidenced. However, in contact with a CEM V pore solution, part of charge-compensating cations (Na+) were substituted by potassium ions (K+), which should not impact negatively the geopolymer paste

Investigation by neutron diffraction of texture induced by the cooling process of zirconia refractories

International audienceNew fused cast refractories with a high content of zirconia have been developed to face corrosion in glass furnaces. The controlled cooling process is responsible for thermal gradients. So, thermal mismatches appear between core and edge zones of blocks. Besides, the multiphasic nature of ZrO2 based refractories is associated to thermal mismatches during cooling. Finally, the expansive transformation of ZrO2 can lead to stress generation.This paper is an application of neutron diffraction to study texture generated during the cooling process of zirconia based materials. In fact, it is shown that ZrO2 crystallographic variants have particular crystallographic texture regarding the main direction of the thermal gradient in the block. It was hypothesized that a selection of crystallographic variants could be done depending on the field stress. Tensile-compressive tests at high temperature have been done, to reproduce stress environment during the transformation of zirconia

Mechanical properties of hemp-lime reinforced mortars: influence of the chemical treatment of fibers

International audienceIn addition to being an environmental-friendly material, hemp fibers are also inexpensive reinforcements in thermoplastics or concrete composites, due to their intrinsic mechanical, thermal, and acoustic properties. However, chemical treatments of fibers are required to enhance the matrix/fiber interface. In this article, the influence of the addition of hemp fibers chemically treated or not, on the mechanical properties of a lime composite was investigated. Mechanical properties were evaluated by ultrasonic pulse echography and four-point bending test associated with acoustic emission analysis. The physical and chemical surface modifications of the hemp fibers were monitored with gas chromatography and scanning electron microscopy. It appears that chemical modification of the fiber surface degrades the amorphous materials present in the fiber structure, which results in an increase in the surface reactivity and also improves the mechanical properties of the composites

Numerical modelling of sulfuric acid attack on OPC and CAC materials

A reactive transport model was developed using HYTEC to simulate sulfuric acid attack on cementitious materials. The model was tested on ordinary Portland cement (OPC) and calcium aluminate cement (CAC) matrices using two sulfuric acid solutions at pH 3 and 1 for 100 days. The main results were that the cumulative leached Ca2+ per initial total Ca2+ was controlled by diffusion mechanisms as it increases linearly versus the square root of time. CAC exhibited a better performance, compared to OPC, at pH 3 while it suffered more deterioration at pH 1. Ettringite precipitation was observed in the decalcified zone with gypsum formation detected on surface only at pH 1. Moreover, the analyses of the solid phases’ profiles after 100 days revealed that the dissolution of AH3 in CAC material accounted for the severe deterioration of the matrix at pH 1. Moreover, an optimization of the numerical model to represent the associated laboratory test – BAC-test [Peyre-Lavigne et al. 2015, 2016] – using a 1D model was validated. Furthermore, a brief comparison of the results obtained by two different numerical models (Aquasim and HYTEC) was presented to highlight the main differences – such as database, reactions of hydrated phases and the diffusion in the porous medium – between the two approaches