Martin Cyr

Abstract: Mixed glasses of different colors are economically difficult to reuse for the fabrication of new glass products but their use in cement-based materials is a promising way to recycle this material. This paper deals with the pozzolanic activity of mixed glass cullet, by evaluating the pozzolanic behavior of a large range of glass particle sizes, from less than 40 µm (540 m2/kg) up to 2.5 mm (2.2 m2/kg). Five different classes of glass are assessed separately, in terms of compressive strength tests on mortars, consumption of lime (TG), morphology (SEM) and composition of hydrates (EDX and X-ray fluorescence). The results show that the pozzolanic activity increases with glass fineness and that, compared to a reference material without glass, equivalent or superior compressive strength can be obtained when using up to 40% of glass of 540 m2/kg fineness. A transition fineness around 30 m2/kg (140 µm) is highlighted, for which the pozzolanic activity becomes substantial. However, a slight but significant pozzolanic activity is detected for coarse particles (>1 mm), as confirmed by the consumption of Ca(OH)2, the formation of C-S-H-like hydrates and an increase of 10% (5 MPa) in the compressive strength compared to an inert admixture. The chronology of the reaction (pozzolanic and alkali-reactive) for coarse glass particles is discussed.

Abstract: 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 realised 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), generalization was suggested and the results was 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.

Abstract: This work is part of an overall project for the reassessment of concrete structures damaged by ASR. The paper focuses on developing a laboratory method for expansion tests since the usual tests appear to be difficult to use in expert assessment. The development involves optimizing the storage conditions and the sizes of the specimen and aggregate. A combined effect of the aggregate and specimen sizes on ASR expansion is thus pointed out: for a given mortar, the expansion is lower in small specimens than in large specimens. Therefore, the ratio �specimen size / aggregate size� has to be sufficiently high to decrease this scale effect and obtain relevant measurements. The discussion proposes a method for always using comparable conditions during the expansion tests and finally suggests how this test can be optimized to provide fast and relevant results for use in structure reassessment.

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 Hadjar slag 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.

Abstract: This work presents the results of experiments aiming to produce geopolymers from glass cullet, a non-traditional material compared to those usually found in the manufacture of geopolymers (e.g. metakaolin and fly ash). The study gives the principal formulation parameters affecting the behavior of glass cullet geopolymers. The glass used comes from recycled glass bottles. The parameters studied are the fineness of the glass (Blaine of 1000 to 4000 cm2/g), the temperature of synthesis (20, 40 and 60°C), and the nature and concentration of the activation product (KOH, NaOH). The properties are evaluated in terms of compressive strength and durability. The results show that cullet of soda-glass can be used as a base material for the production of geopolymers and, contrary to metakaolin-based geopolymers, no waterglass is necessary for its setting and hardening since cullet glass already contains a high proportion of alkalis. Thermal activation at 40 or 60°C is necessary but sufficient to obtain strength of more than 50 MPa, especially for the finer glass (4000 cm2/g). The durability of glass cullet geopolymers is affected by water conservation.

Abstract: Attempts to model ASR expansion are usually limited by the dif fi culty of taking into account the heterogeneous nature and size range of reactive aggregates. This work is a part of an overall project aimed at developing models to predict the potential expansion of concrete containing alkali-reactive aggregates. The paper gives measurements in order to provide experimental data concerning the effect of particle size of an alkali-reactive siliceous limestone on mortar expansion. Results show that no expansion was measured on the mortars using small particles (under 80 µm) while the coarse particles (0.63�1.25 mm) gave the largest expansions (0.33%). When two sizes of aggregate were used, ASR-expansions decreased with the proportion of small particles. Models are proposed to study correlations between the measured expansions and parameters such as the size of aggregates and the alkali and reactive silica contents. The pessimum effect of reactive aggregate size is assessed and the consequences on accelerated laboratory tests are discussed.

Abstract: Demand for recycled glass has considerably decreased in recent years, particularly for mixed glass. Glass is cheaper to store than to recycle, as conditioners require expenses for the recycling process. In order to provide a sustainable solution to glass storage, a potential and incentive way would be to reuse this type of glass in concretes. Depending on the size of the glass particles used in concrete, two antagonistic behaviours can be observed: alkali�silica reaction, which involves negative effects, and pozzolanic reac- tion, improving the properties of concrete. The work undertaken here dealt with the use of fine particles of glass and glass aggregates in mortars, either separately or combined. Two parameters based on stand- ardised tests were studied: pozzolanic assessment by mechanical tests on mortar samples and alkali- reactive aggregate characteristics and fines inhibitor evaluations by monitoring of dimensional changes. It is shown that there is no need to use glass in the form of fines since no swelling due to alkali�silica reaction is recorded when the diameter of the glass grains is less than 1 mm. Besides, fine glass powders having specific surface areas ranging from 180 to 540 m 2 /kg reduce the expansions of mortars subjected to alkali�silica reaction (especially when glass aggregates of diameters larger than 1 mm are used).

Abstract: The objective of the work presented in this paper is the quantitative determination of the mineral com- position of two complex mineral wastes: a sewage sludge ash (SSA) and a municipal solid waste inciner- ation 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 phys- icochemical 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 crystallog- raphy. So the use of another, complementary, method such as the first one used in this study, may some- times be needed to confirm the results.

Abstract: The objective of this study was the synthesis of a'L-C2S (Ca2SiO4) belite cement, starting from fly-ash of system CaO�SiO2 �Al2O3�SO3 , and using the hydrothermal method in alkaline solution. The lime deficit in these ashes was compensated by the addition of slaked lime from lime bagging workshops. The hydrother- mal treatment of the mixture was carried out in demineralized water, NaOH or KOH solution, continually stirred at a temperature below 100°C and atmospheric pressure. The dehydration and calcination of the mixtures at temperatures between 800 and 1100°C allowed a'L-C2S-rich cement to be obtained. The optimization of the synthesis parameters (temperature and time of stirring, pH of solution, temperature and duration of mixture burning) was also studied. The phase formation during various synthesis stages was studied by X-ray diffraction (XRD). Other techniques, such as SEM and EDX, were used to characterize the cement minerals. The results obtained showed that these ashes could form belite cement composed of only one dicalcium silicate phase (a'L-C2S).

Abstract: Since 1964, the Temple-sur-Lot Dam, built in southwest France in 1948, has been subject to continuous alkali-aggregate reaction (AAR)-induced displacements despite low and relatively constant alkali content in the concrete and nonsignificant residual swelling test results. It has been assumed that a substitution process between alkali and calcium in the alkali-aggregate reactive gel could explain this long-term behavior. As the calcium substitution phenomenon is very slow, it cannot be detected using a conventional residual swelling test, so an original method to assess the AAR kinetics and the residual swelling capability is proposed. This method first involved a laboratory test dealing with the silica consumption kinetics and, second, a numerical finite element inverse analysis of the dam, which included the consumption kinetics measured in the laboratory. The final swelling amplitude was thus fitted from only one observed structural displacement rate at a given period. The model prediction capability was validated through the comparison between the displacement of instrumented points predicted by the calculations (not used for the fitting) and the variations measured on the dam. Finally, calculations were performed to predict the future displacements and damage fields of the dam.

Abstract: 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 Cd2+/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 Cd2+ is mainly immobilized as Ca10 � xCdx(PO4)6(OH)2 by both ashes, whereas otavite, Cd(CO3), 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 2 mg Cd2+/L. However addition of only 0.1 g/L MBM-LA inhibits these effects for the above concentration values whereas Cd2+ bioaccumulation in larvae's liver is similar for both experiments, with and without ashes.

Abstract: The effect of the size of the aggregate on ASR expansion has already been well illustrated. This paper presents a microscopic model to analyze the development of ASR expansion of mortars containing reactive aggregate of different sizes. The attack of the reactive silica by alkali was determined through the mass balance equation, which controls the diffusion mechanism in the aggregate and the fixation of the alkali in the ASR gels. The mechanical part of the model is based on the damage theory in order to assess the decrease of stiffness of the mortar due to cracking caused by ASR and to calculate the expansion of a Representative Elementary Volume (REV) of concrete. Parameters of the model were estimated by curve fitting the expansions of four experimental mortars. The paper shows that the decrease of expansion with the size of the aggregate and the increase of the expansion with the alkali content are reproduced by the model, which is able to predict the expansions of six other mortars containing two sizes of reactive aggregate and cast with two alkali contents.

Abstract: This study assesses the potential of ground reactive aggregates to reduce or suppress expansion associ- ated with ASR. Particular attention is paid to fine admixtures (<80 lm) added to mortars, which contain the reactive aggregates from which the fines were ground. Many varieties of aggregate (quarried and nat- ural, igneous, metamorphic and sedimentary rocks) from different geological settings were subjected to an autoclave test. The replacement of 10�20% of the sand by reactive aggregate powder (RAP) of different surface areas from 11 different reactive aggregates led to the reduction of ASR-expansion by up to 78% compared with control mortars. Increasing the amount of fines led to better performance. No clear rela- tionship was observed between the reactivity degree of the aggregates and the efficiency of their ground powder to reduce expansion. A general trend was found regarding the fineness of ground aggregates: finer particles were more effective in reducing expansion. The reduction of the expansion due to RAP is discussed in terms of parameters affecting its efficiency and of the mechanisms responsible for the reduction.

Abstract: This paper deals with the application of a performance-based approach on the durability of concrete made with an Algerian natural pozzolan. The evaluation of the durability of concrete was based on the comparison of durability indicators with a reference concrete usually found in Algeria. The properties measured included general indicators (water porosity, gas permeability, capillary absorption and Portlan- dite content) and specific indicators related to degradation phenomena that might occur in Algeria: cor- rosion induced by carbonation and chlorides, and chemical attacks by sulphates and acids. For the specific degradations, the indicators measured included carbonation depths, chloride diffusion coefficients, chlo- ride permeability, expansion and sulphate profiles, and depth of leaching due to ammonium nitrate attack. The results showed that general durability indicators were almost equivalent for all the types of concrete tested, highlighting the importance of using specific indicators for each type of exposure. The results of specific indicators for corrosion and acid attacks showed that increasing the pozzolan con- tent led to higher resistance of the concrete. Thus, it is possible to improve the durability of typical con- cretes currently made in Algeria by using local materials.

Abstract: This paper aims to evaluate the potential of a natural Algerian pozzolan for use in cement-based materials. This pozzolan can be classified in the group of pyroclastic rocks, like the Italian pozzolan, and that it respected the specifications for natural pozzolans as given in American (ASTM C618), Canadian (A3001), French (NF P 18-308) and Algerian (NA 2830) standards. The effects of the pozzolan on the fresh state of mortars showed that it led to an increase in water demand and a slight increase in setting time. For hardened mortars, the long-term strengths were higher for replacement rates of up to 30%, without increasing the free shrinkage of prisms. These results appear to show that it is possible to obtain cement-based materials having correct properties by using only 70% of cement, thus confirming the interest of this kind of material, especially in developing countries.

Abstract: This study aimed to evaluate the effectiveness of a mechanism responsible for the mitigation of expansion when reactive aggregate powders (RAP) were used in concrete containing the same reactive aggregate. In the first part, it was shown that RAP were efficient in reducing the expansion of concrete by 35 to 95%. The most efficient powders were those coming from aggregates having high active silica contents (glass, opal). Powders of siliceous limestone were less effective. In a second part, experimental evidence of the pozzolanic activity of RAP was obtained. It was shown that RAP were similar to pozzolan, since they consumed lime and produce calcium� silicate�hydrate (C�S�H) having a lower calcium/silica (C/S) ratio than normal C�S�H. The third part showed experimentally that these low C/S C�S�H could increase the redistribution of alkalis of the pore solution, thus reducing the alkalinity of the pore solution to a level that was sufficiently low to limit the attack of coarser reactive aggregates. In the final part, numerical simulations using a modified version of the hydration model CEMHYD3D were carried out to support this assumption.

Abstract: A high-pressure device, reaching an axial pressure of 1000 MPa, intended to the extraction of the pore solution of rigid and slightly porous materials, has been developed to improve the efficiency of extraction. This paper gives an application of fluid extraction from mortars made with Portland cement. It includes an experimental study of the performance of the apparatus, and an analysis of the results in terms of efficiency of extraction, repeatability of measurement, and effect of the squeezing pressure on the pore solution composition. Results shows that: (1) the squeezing efficiency using our apparatus is higher than those found in the literature; (2) the measurement uncertainty ranges between 1.5% and 14%; (3) no significant effect of pressure (up to 1000 MPa) is observed for concentrations of Ca, Na, K, and Si. This paper suggests conducting extraction at 1000 MPa, especially on old concrete or concrete made with low W/C ratios.

Abstract: This paper reports the characterization of four meat and bone meal (MBM) ashes obtained from specific incineration (laboratory) and from co-incineration (industrial process). Three out of the four MBM ashes were mainly composed of calcium phosphates (hydroxyapatite and whitlockite). Their compositions (major and trace) were in the range for natural phosphate rocks. Trace element contents, including heavy metals, were below 0.6% and industrial ashes contained much more heavy metals than laboratory ash. The amounts of leached elements were low, especially for laboratory ash. According to the European classification of waste to be landfilled, the laboratory ash can be classified as an inert waste. Two industrial ashes are mostly inert. Only one ash is highly leachable and needs a stabilization treatment to be classified at least in the category of hazardous waste. It seems, from these results, that possibilities other than landfilling could be considered to give economic value to these ashes. (c) 2007 Elsevier B.V. All rights reserved.

Abstract: This work is a part of an overall project aimed at developing models to predict the potential expansion of concrete containing alkali-reactive aggregates. First, this paper reports experimental results concerning the effect of particle size of an alkali-reactive siliceous limestone on mortar expansion. Special attention is paid to the proportions of alkali (Na2Oeq) in the mixtures and reactive silica in the aggregate. Results show that ASR expansion is seven times larger for coarse particles (1.25-3.15 mm) than for smaller ones (80-160 mu m). In mortars for which the two size fractions were used, ASR expansion increased in almost linear proportion to the amount of coarse reactive particles, for two different alkali contents. Then, an empirical model is proposed to study correlations between the measured expansions and parameters such as the size of aggregates and the alkali and reactive silica contents. Starting with the procedure for calibrating the empirical model using the experimental program combined with results from the literature, it is shown that the expansion of a mortar containing different sizes of reactive aggregate can be assessed with acceptable accuracy. (C) 2007 Elsevier Ltd. All rights reserved.

Abstract: A possible practice to prevent disorders due to alkali-silica reaction (ASR) in concretes containing reactive aggregates is the use of chemical admixtures (lithium salts) or, more commonly, mineral admixtures such as fly ash, silica fume, ground granulated slag or metakaolin. An analysis of the literature concerning ASR revealed some papers devoted to the mitigating activity of reactive aggregate powders (RAP) when associated with their parent aggregates. These RAP result from the grinding of the reactive aggregate. To verify the efficiency of this method of mitigation, tests were performed on concrete prisms cured at 60 degrees C and 100% R.H., using four reactive aggregates, associated or not with their RAP. The results showed that the use of RAP reduced or suppressed ASR-expansion, suppressed surface cracking and counteracted the loss of compressive strength due to ASR. If these findings are confirmed by trials on other types of aggregates, the addition of RAP would be a simple way of avoiding ASR disorders.

Abstract: 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. (c) 2007 American Institute of Physics.

Abstract: Sewage sludge ash (SSA) is a waste material obtained from the incineration of wastewater sludge. The physical, chemical and mineralogical characteristics of SSA, and the evaluation of its use in cement-based materials, are presented in this paper. Results show that SSA is composed of irregular grains having a high specific surface area and thus leading to a significantly high water demand. A fraction of the ash is rapidly soluble (sulfates, aluminum and silica) and can create new-formed products in presence of lime. SSA induces short delays of cement hydration, probably due to both minor elements of the ash and dilution effect. Compressive strengths of mortars containing 25% and 50% of SSA are always lower than those of reference mortars but it is shown that SSA has a long-term positive effect which might be related to a slight pozzolanic activity. The amount of elements leached from SSA mortars is slightly higher than from the reference mortar without residue but it remains of the same order of magnitude. An extensive literature review was performed in order to compare the residue used in this study with others included in the same category. This analysis highlighted the principal characteristics that must be taken into account to use SSA correctly in cement-based materials. (c) 2007 Elsevier Ltd. All rights reserved.

Abstract: The effects of partial replacements (5%, 10%, 15% and 20%) of Portland cement by high-purity metakaolin (MK) on the autogenous shrinkage of pastes (water/binder ratios 0.3 and 0.5) were investigated. In order to distinguish the effect of heterogeneous nucleation and pozzolanic activity from the dilution effect, some mixes were prepared using a coarse powder (Q(ref)) instead of MK (10% and 20% for both w/b ratios). The hydration of cement-MK pastes was followed qualitatively by differential thermal analysis (DTA). DTA showed that C-S-H and gehlenite (C(2)ASH(8)) were the main compounds produced by MK pozzolanic reaction. Results showed that the long-term autogenous shrinkage of cement-MK pastes, for both w/b ratios, decreased as the cement replacement level by MK increased. No expansion was observed at early ages, contrary to the findings of other authors. With the elimination of the dilution effect, it was shown, at early ages, that the increase of autogenous shrinkage of the cement-MK pastes relative to cement-Q(ref) mixes was due to heterogeneous nucleation. At later ages, autogenous shrinkage became lower for cement-MK pastes than for cement-Q(ref) pastes, surely because the pozzolanic activity of MK became predominant. This behavior i.e. reduction of autogenous shrinkage, is one more benefit confirming the interest of using MK in concrete. (c) 2006 Elsevier Ltd. All rights reserved.

Abstract: This paper presents the physical, chemical and mechanical characteristics of sewage sludge ash (SSA), in order to compare its properties with the standard requirements for coal fly ash (FA). It also provides an evaluation of its environmental behaviour when used as a mineral admixture in cement-based materials. Results show that, compared with FA, SSA has a high amount of calcium and phosphorus but a relatively low fraction of silica. SSA is composed of irregular grains having a high specific surface area and thus leading to a high water demand. The high water absorption of SSA requires an increase of the water�binder ratio of mortars, or the use of a water-reducing admixture. The strength activity index (25% replacement of cement) reaches more than 90% after 28 days, showing a long-term positive effect, which might be related to the pozzolanic activity. The amount of leached elements of SSA mortars is slightly higher than for the reference mortar without residue, but it remains within the same order of magnitude. The comparison of the characteristics of SSA with the FA specifications given by American and European standards shows that SSA does not satisfy the requirements to be directly considered as a mineral admixture. Nevertheless, these preliminary results show that SSA could be classified between filler and pozzolanic admixtures. Thus SSA may not necessarily be excluded from use in cement-based materials.

Abstract: This work is the fourth part of an overall project the aim of which was the development of general mix design rules for concrete containing different kinds of mineral admixtures. The two first parts presented the separation and quantification, by means of an empirical model based on semi-adiabatic calorimetry measurements, of the different physical effects responsible for changes in cement hydration (short terms) when chemically inert quartz powders were used in mortars. Part three dealt with an intensive experimental program, presenting and commenting more than 2000 compressive strength measurements. This program concerned 1 day to 6 months old mortars containing up to 75% of inert and pozzolanic admixtures. All these compressive strength results are analyzed in this fourth part and the influence of three effects, namely dilution, heterogeneous nucleation and the pozzolanic effect, are discriminated and quantitatively evaluated. An efficiency concept is proposed in order to take into account the effect of mineral admixture in mortars from both the physical and chemical points of view. It uses an efficieney function xi(p) that has notable properties: it is independent of time, independent of fineness and independent of the type of mineral admixture. (c) 2005 Elsevier Ltd. All rights reserved.

Abstract: This paper, which enters in a sustainable development approach, aims to present a method developed by Laboratoire Mat?riaux et Durabilit? des Constructions (LMDC) in Toulouse, for the assessment of the recycling of waste as secondary raw materials in cementbased materials used in civil engineering applications. The approach includes two parts carried out simultaneously: (i) a technological part, the aim of which is the evaluation of the effect of wastes on the chemical, physical and mechanical properties of fresh and hardened concrete; (ii) an environmental part, mainly based on leaching tests, in order to evaluate the environmental impact of wastes used in concrete materials. The method is illustrated with various cases taken from past studies performed in LMDC.

Abstract: This paper presents the physical, chemical and mineralogical characteristics of meat and bone meal bottom ash (MBM-BA) from low-risk sources. It also gives a first evaluation, from a technical and an environmental point of view, of its potential of use as sand in cement-based materials. Results show that MBM-BA has the physical characteristics of a fine sand. It has low friability but high water absorption, which leads to a recommended use of less than 30% MBM-BA as sand replacement in mortars and the use of a superplasticizer. The compressive strength of mortar containing 17% of MBM-BA is similar to that of a reference mortar and the leaching behavior resembles that of the reference mortar without residue, These preliminary results lead us to believe that low-risk MBM-BA could be used in cement-based materials and present a promising way of reusing this residue. (c) 2005 Elsevier Ltd. All rights reserved.

Abstract: This work is the second 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 first part presented the separation of the different physical effects responsible for changes in cement hydration when chemically inert quartz powders are used in mortars. This second part describes the development of an empirical model, based on semiadiabatic calorimetry measurements, which leads to the quantification of the enhancement of cement hydration due to the heterogeneous nucleation effect at short hydration times. Experimental results show that not all the admixture particles participate in the heterogeneous nucleation process. Consequently, the concept of efficient surface S-eff is introduced in the-model. S-eff is the total admixture surface S (m(2) of mineral admixture/kg of cement) weighted by a function xi(p). The efficiency function xi(p) depends only on the replacement rate p and is independent of time, fineness and type of mineral admixture used. It decreases from 1 to 0: Low replacement rates give an efficiency value near 1, which means that all admixture particles enhance the hydration process. An efficiency value near 0 is obtained for high replacement rates, which indicates that, from the hydration point of view, an excess of inert powder does not lead to an increase in the amount of hydrates compared with the reference mortar without mineral admixture. The empirical model, which is mainly related to the specific surface area of the admixtures, quantifies the variation of the degree of hydration induced by the use of inert mineral admixtures. One application of the model, coupled with Powers' law, is the prediction of the short-term compressive strength of mortars. (c) 2004 Elsevier Ltd. All rights reserved.

Abstract: This work is the third 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 (also named mineral additions or mineral constituents). It deals with the compressive strength of mortars made with up to 75% of crushed quartz, limestone filler or fly ash of different fineness. The paper presents all the experimental results as a sort of database and emphasizes the effects on strength of the nature, amount and fineness of mineral admixtures. For short hydration times (1 to 2 days), the nature of mineral admixture is not a significant parameter, as mortars containing the same amount of different kinds of admixtures having equivalent fineness present similar strengths. For long hydration times (up to 6 months), the excess strength due to fly ash pozzolanic activity is quantified by the difference between the strengths of mortars containing the same proportions of inert and pozzolanic admixtures with the same fineness. In the case of inert mineral admixtures, the increase in strength with the fineness of mineral admixtures cannot be explained by the filler effect, but can be attributed to the physical effect of heterogeneous nucleation. In the next part of this work, these results will be used for the elaboration of an empirical model leading to the quantification of both physical and chemical effects. This model presents strong similarities with the previous model based on calorimetric results. (c) 2004 Elsevier Ltd. All rights reserved.

Abstract: 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 m(2)/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. (C) 2003 by Elsevier Science Ltd. All rights reserved.

Abstract:

Abstract: This paper presents a method for assessing the normalized age factors. which allow accelerated alkali-aggregate reaction (AAR) tests performed at various temperatures (20, 40 and 60 degreesC) to be related to the conditions encountered in situ in concrete structures. The evaluation of normalized age factors is based on the comparison of many experimental results taken from the literature concerning laboratory tests and in situ measurements. The use of these factors permits us to evaluate. from the results of an accelerated test performed at 60 degreesC, the protection time against AAR that could be expected for in situ concretes containing mineral admixtures (silica fume and fly ashes). The results show that, in addition to the inhibitory action of mineral admixtures leading to a strong decrease in the final AAR-swelling, the protection against abnormal expansion caused by AAR increases significantly when mineral admixtures are used. Abnormal expansion is expected at 2-4 years for plain concrete compared to 7-50 years for concrete with mineral admixtures. (C) 2002 Elsevier Science Ltd. All rights reserved.

Abstract: 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 x 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. (C) 2002 Elsevier Science Ltd. All rights reserved.

Abstract: LASER diffraction spectrometry is one of the most widespread techniques for particle sizing, but it must be used with many precautions, otherwise significant errors can be expected. Generally, the most important errors concern the evaluation of the fine (smaller than some microns) particle content and they are obtained when the particles move away from ideal conditions (which are spherical particles, monophasic and isotropic material). Among the various sources of errors and inaccuracies concerning this technique, two have been dealt with in this paper: the choice of the mathematical model and the evaluation of the optical properties of the materials analyzed. Practical cases are presented, which permit to evaluate the consequences of these errors, such as calculation of virtual fine particles that do not exist. Lastly, precautionary measures are suggested to minimize the errors and thus to increase the degree of confidence in the results. In all the cases studied, it was seen that a correct evaluation of particle size distribution by this technique required substantial preliminary knowledge of the physicochemical properties of the material.

Abstract: A series of characterization experiments was conducted to evaluate two by-products from the iron and titanium industry (ilmenite fines and titanium fume) to be use in cement-based materials. Although these by-products show a weak reactivity (early age), their physical properties, especially in the case of titanium fume, which is formed of spherical particles with a mean particle diameter of 1.7 mu m, lead to an enhancement of the mechanical strength of mortars (for mortars containing up to 5% replacement of cement). For larger substitution rates, their efficiency coefficients stand between those of inert and pozzolanic materials. (C) 2000 Elsevier Science Ltd. All rights reserved.

Abstract: The decision of public authorities to recycle industrial wastes leads to the quasi-systematic use of mineral admixtures in concrete. Predicting the strength of these concretes induces the engineer to characterise the mineral admixtures: ordinarily, a single coefficient is used, calculated with an empirical law like Bolomey's or Abrams' formulas. Many results, reported in bibliography and completed by the authors, show that the determination of this single coefficient is not sufficient to characterise the activity of the admixture. Many factors like the nature of cement, the substitution rate, the fineness of the admixture and the age of concrete induce a great variability of the efficiency coefficient of the admixtures. Up to now, there is no general law explaining this variability. The authors warn against the excessive use of a single equivalence coefficient and recommend to take into account not only the physicochemical parameters but also the nature of the works themselves.

Abstract: Fresh cement pastes, when dispersed by a superplasticizer acting mainly by electrostatic effect, present a viscosity that increases with the shear rate (shear thickening). When mineral additives are used, the intensity of the phenomenon depends on their nature: it can be amplified (metakaolin), unchanged (quartz, fly ashes) or reduced (silica fumes). According to the literature, shear thickening occurs when suspensions have a high solid concentration and when repulsive interactions are predominant. These conditions can be achieved in cement pastes owing to the dispersing action of superplasticizer. In that case, the shear thickening behaviour could be due to local mechanical actions created by the increased shearing forces. (C) 2000 Elsevier Science Ltd. All rights reserved.

Abstract: Usually, quantitative determination of amorphous phase in materials is obtained by subatracting, from 100%, the sum of all crystallised minerals calculated by classical QXRD methods. There is some interest in developping XRD methods: that will permit either to directly evaluate amorphous content of these materials or to simplify existing indirect methods. The purpose of this paper is to develop new methods (direct and indirect) for the determination of amorphous content in synthetic and industrial materials. The application of the foul methods proposed on ten different materials lead to consistent results, with a precision up to a few percent. This level of precision is usually adequate for most civil engineering applications.