Martin Cyr

Mineral admixtures in mortars Effect of inert materials on short-term hydration

This work is the first part of an overall project the aim of which is the development of general mix design rules for concrete containing different kinds of mineral admixtures. The separation of the different physical effects responsible for the modification of cement hydration, when chemically inert quartz powders are used in mortars, is presented. The phenomenological approach, based on semi-adiabatic calorimetry, is only associated with first-order phenomena, and the study excludes the complex physicochemical details involved in the chemistry of cement. The results, obtained for a wide range of fineness (between 180 and 2000 m2/kg) and replacement rates (up to 75%), show that short-term degrees of hydration in mortars containing a chemically inert mineral admixture (quartz) are always higher than for a reference mortar. This study confirms that cement hydration is enhanced by inert mineral admixtures. The two main physical effects responsible for the modification of the hydration of cement are identified as the dilution effect and heterogeneous nucleation. The dilution effect of the cement is highlighted with a coarse mineral admixture. The heterogeneous nucleation effect, although it increases with fineness of mineral admixtures, presents an optimum depending on the replacement rate. In the following part of this work, these results will be used for the development of an empirical model allowing us to quantify both physical effects.

Use of metakaolin to stabilize sewage sludge ash and municipal solid waste incineration fly ash in cement-based materials.

The landfilling of municipal incineration residues is an expensive option for municipalities. This work evaluates an alternative way to render waste inert in cement-based materials by combining the reduction of waste content with the immobilization properties of metakaolin (MK). The functional and environmental properties of ternary and quaternary binders using cement, metakaolin, and two industrial by-products from combustion processes (MSWIFA - Municipal Solid Waste Incineration Fly Ash and SSA - Sewage Sludge Ash) were evaluated. The binders were composed of 75% cement, 22.5% metakaolin and 2.5% residue. Results on the impact of residues on the functional and environmental behavior of mortars showed that the mechanical, dimensional and leaching properties were not affected by the residues. In particular, the use of metakaolin led to a significant decrease in soluble fractions and heavy metals released from the binder matrix. The results are discussed in terms of classification of the leaching behavior, efficiency and role of metakaolin in the immobilization of heavy metals in of MSWIFA and SSA, and the pertinence of the dilution process.

Combination of Structural Monitoring and Laboratory Tests for Assessment of Alkali-Aggregate Reaction Swelling: Application to Gate Structure Dam

Southwestern Frances Temple-sur-Lot Dam, a gate structure built in 1948, has been subjected to continuous alkali-aggregate reaction (AAR)-induced displacements since 1964, despite nonsignificant residual swelling test results and low and relatively constant alkali content in the concrete. It has been assumed that this long-term behavior could be explained through a substitution process between calcium and alkali in the alkali-aggregate reactive gel. The calcium substitution phenomenon cannot be detected through a conventional residual swelling test since it is very slow, so an original AAR kinetics and residual swelling capability assessment method is proposed. A laboratory test dealing with silica consumption kinetics is first involved in this methods, and a numerical finite element inverse dam analysis, including laboratory measured consumption kinetics, is involved as a second step in this method. At a given period, only one observed structural displacement rate fit the final swelling amplitude. Comparison between instrument point displacement predicted by the calculations (not used for the fitting) and dam measured variations provided model prediction capability validation. Finally, future dam displacement and damage field prediction calculations were performed.

Quantitative mineralogical composition of complex mineral wastes – Contribution of the Rietveld method

The objective of the work presented in this paper is the quantitative determination of the mineral composition of two complex mineral wastes: a sewage sludge ash (SSA) and a municipal solid waste incineration fly ash (MSWIFA). The mineral compositions were determined by two different methods: the first based on calculation using the qualitative mineralogical composition of the waste combined with physicochemical analyses; the second the Rietveld method, which uses only X-ray diffraction patterns. The results obtained are coherent, showing that it is possible to quantify the mineral compositions of complex mineral waste with such methods. The apparent simplicity of the Rietveld method (due principally to the availability of software packages implementing the method) facilitates its use. However, care should be taken since the crystal structure analysis based on powder diffraction data needs experience and a thorough understanding of crystallography. So the use of another, complementary, method such as the first one used in this study, may sometimes be needed to confirm the results.

Interpretation of expansion curves of concrete subjected to accelerated alkali–aggregate reaction (AAR) tests

The examination of several long-term expansion results for concretes subjected to accelerated alkali–aggregate reaction (AAR) tests shows that, in some cases, the expansion continues for a long time after AAR has stopped. For these cases, all the concrete swelling is certainly not only caused by AAR, and the continuation of the expansion probably reveals the swelling behavior of concrete when it is conserved in saturated moisture conditions. Considering that this swelling is not negligible compared to the limit expansions fixed by standard AAR tests (2×10−4 at 90 days for the French performance test), it becomes important to evaluate it in order to avoid the inappropriate rejection of an aggregate.

Evaluation of laboratory and industrial meat and bone meal combustion residue as cadmium immobilizing material for remediation of polluted aqueous solutions: Chemical and ecotoxicological studies

Meat and Bone Meals (MBM) combustion residues (ashes) are calcium and phosphate-rich materials. The aim of this work is to evaluate ashes efficiency for remediation of cadmium-contaminated aqueous solutions, and to assess the bioavailability of cadmium on Xenopus laevis larvae. In this study both industrial (MBM-BA) and laboratory (MBM-LA) ashes are compared regarding their efficiency. Kinetic investigations reveal that cadmium ions are quickly immobilized, with a maximum cadmium uptake at 57 mg Cd(2+)/g of ashes for MBM-LA, two times higher than metal uptake quantity of MBM-BA, in our experimental conditions. Chemical and X-ray diffraction analysis (XRD) reveal that Cd(2+) is mainly immobilized as Ca(10-x)Cd(x)(PO(4))(6)(OH)(2) by both ashes, whereas otavite, Cd(CO(3)), is also involved for MBM-LA in cadmium uptake. Otavite formation could be explained by the presence of carbonates in MBM-LA, as observed by IR. Genotoxicity of cadmium solution on Xenopus larvae is observed at 0.02, 0.2 and 2mg Cd(2+)/L. However addition of only 0.1g/L MBM-LA inhibits these effects for the above concentration values whereas Cd(2+) bioaccumulation in larvaes liver is similar for both experiments, with and without ashes.

Quantification of uncertainty of experimental measurement in leaching test on cement-based materials.

When mineral wastes are reused in construction materials, a current practice is to evaluate their environmental impact using standard leaching test. However, due to the uncertainty of the measurement, it is usually quite difficult to estimate the pollutant potential compared to other materials or threshold limits. The aim of this paper is to give a quantitative evaluation of the uncertainty of leachate concentrations of cement-based materials, as a function of the number of test performed. The relative standard deviations and relative confidence intervals are determined using experimental data in order to give a global evaluation of the uncertainty of leachate concentrations (determination of total relative standard deviation). Various combinations were realized in order to point out the origin of large dispersion of the results (determination of relative standard deviation linked to analytical measured and to leaching procedure), generalisation was suggested and the results were compared to literature. An actual example was given about the introduction of residue (meat and bone meal bottom ash--MBM-BA) in mortar, leaching tests were carried out on various samples with and without residue MBM-BA. In conclusion large dispersion were observed and mainly due to heterogeneity of materials. So heightened attention needed to analyse leaching result on cement-based materials and further more other tests (e.g. ecotoxicology) should be performed to evaluate the environmental effect of these materials.

Physical and chemical effects of El Hadjar slag used as an additive in cement-based materials

ABSTRACT Granulated blast furnace slag is currently one of the most important sources of materials for the production of blended cements. Since 1999, the use of slag in France has increased by 52% while the increase in clinker production has not exceeded 13%. In times of shortage, the high demand for slag is not always easy to satisfy, and new sources of supply need to be found. The furnace slag of El Hadjar (Annaba, Algeria) comes into this category. The paper deals with the characteristics and reactivity of this slag. A comparison with European slags shows that, although it fulfills all Standards requirements, the El Hadjarslag has slow reaction kinetics. The activity, measured on the compressive strength of mortars whose binder contains 10 to 100% slag of four finenesses ranging from 2500 to 4000 cm2/g, strongly depends on the slag fineness. The activity is quantified by using an approach which separates the effect of cement dilution from the physical and chemical effects of the slag.

Optimization of a high-pressure pore water extraction device

High-pressure squeezing is a technique used for the extraction of the pore water of porous materials such as sediments, soils, rocks, and concrete. The efficiency of extraction depends on the maximum pressures on the materials. This article presents the design of a high-pressure device reaching an axial pressure of 1000 MPa which has been developed to improve the efficiency of extraction. The increase in squeezing pressure implies high stresses inside the chamber, so specialized expertise was required to design a safe, functional device that could withstand pressures significantly higher than common laboratory equipment. The design includes finite element calculations, selection of appropriate materials, and descriptive construction details for the apparatus. It also includes an experimental study of the performance of the apparatus in terms of extraction efficiency.

Characterization of an Algerian natural pozzolan for its use in eco-efficient cement

The paper presents the characterisation of an Algerian natural pozzolan (NP) intended to for use in cement-based materials. The experimental programme was based on different tests on paste and mortar. The pozzolanic activity was assessed by the means of lime consumption over time of mixtures of lime-pozzolan (75% NP and 25% Ca(OH)(2), water-binder ratio of 0.45). The degree of reactivity was assessed by observing the crystallographic changes (XRD) and lime constumption (TG) up to 1 year of hydration. The effect of NP on cement-based mixtures was based on the measurement of the water demand and setting time of pastes, and on the compressive strength of mortars, up to one year. The replacement rates of cement by pozzolan were 5, 10 and 15%. A superplasticizer was used (0, 1, 2 and 3% of the binder mass). A calculation of the carbon footprint was investigated in order to assess if the natural pozzolan could be considered as eco-efficient when used in replacement of the clinker. The results showed that NP had a medium pozzolanic reactivity and with a medium-low silica content. The use of NP usually led to a small increase in the water/binder ratio (up to 10%) to maintain constant workability. The setting time was also increased by around 20%. Nevertheless, strength tests showed that the pozzolan had sufficient activity to counteract the water demand, since long-term compressive strength of the binary system (cement + pozzolan) were higher than those of cement alone. The use of NP in replacement of clinker involves a reduction in CO2 emissions for transport up to 1800 km, which is compatible with sustainable development. The results are most promising from both a performance-based and an environmental point of view.