Durability and chromatic behavior in cement pastes containing ceramic industry milling and glazing by-products

The decay in mortar and concrete induced by extremely aggressive agents is normally the result of the agent-binder reaction. Cement composition and characteristics therefore determine the durability of the mortars and concretes of which they form part. The existing legislation envisages the use of different types of additions in cement, which have a direct effect on the durability of elements in buildings and civil works. This study addressed the inclusion of ceramic industry milling and glazing sludge as an active addition in cement. The reuse of this industrial waste is consistent with environmental policies that seek to reduce or eliminate spoil heaps by recycling industrial waste and byproducts as raw materials, in keeping with circular economy principles. The research conducted makes an innovative contribution to the valorization of this waste, and highlights the resistance of blended cement pastes to chemical agents, further to the Koch-Steinegger method. Water-induced decay in freeze/thaw situations was also studied. The processes involved were identified by analyzing the mineralogical variations detected with X-ray diffraction, the morphological alterations observed with scanning electron microscopy and the mercury porosimetric findings on pore size distribution. The suitability of these binders for aesthetically demanding applications was also explored by measuring the color in pastes exposed to aggressive chemical agents. For the first time, a correlation was established between color parameters and the formation of the reaction products generated during chemical attack.     

Cement pastes alteration by liquid manure organic acids: chemical and mineralogical characterization

Liquid manure, stored in silos often made of concrete, contains volatile fatty acids (VFAs) that are chemically very aggressive for the cementitious matrix. Among common cements, blast-furnace slag cements are classically resistant to aggressive environments and particularly to acidic media. However, some standards impose the use of low C₃A content cements when constructing the liquid manure silos. Previous studies showed the poor performance of low-C₃A ordinary Portland cement (OPC). This article aims at clarifying this ambiguity by analyzing mechanisms of organic acid attack on cementitious materials and identifying the cement composition parameters influencing the durability of agricultural concrete. This study concentrated on three types of hardened cement pastes made with OPC, low-C₃A OPC and slag cement, which were immersed in a mixture of several organic acids simulating liquid manure. The chemical and mineralogical modifications were analyzed by electronic microprobe, XRD and BSE mode SEM observations. The attack by the organic acids on liquid manure may be compared with that of strong acids. The alteration translates into a lixiviation, and the organic acid anions have no specific effect since the calcium salts produced are soluble in water. The results show the better durability of slag cement paste and the necessity to limit the amount of CaO, to increase the amount of SiO₂ (i.e., reduction of the Ca/Si ratio of C-S-H is not sufficient) and to favor the presence of secondary elements in cement.     

Influence of chloride ions and pH level on the durability of high performance cement pastes

The resistance to chemical attack of low water to binder ratio pastes containing silica fume was studied by soaking small paste disks in three different pH controlled solutions, with or without sodium chloride, for periods of up to three months. The pastes were made using water to binder ratios of 0,25 and 0,38. The three solutions in which the paste disks were soaked were the following: 3% NaCl (by weight) at a pH level of 8,5,0% NaCl at 8,5, and 0% NaCl at 4,5. After three months of exposure, the results show that the pH level of the aggressive solution is the most important factor controlling the durability of cement pastes subjected to chemical attack. The total porosity and the depth of decalcification was found to increase with the decrease of the pH level. It was also found that the3water to binder ratio does not significantly affect the deterioration processes, but only influences the kinetics of these processes. The decrease of the water to binder ratio reduces significantly the rate of deterioration. Chloroaluminate crystals were observed only in the cement pastes having a water to binder ratio of 0,38.     

Durability of Blended Cement Pastes Containing Ceramic Waste as a Pozzolanic Addition

Durability is one of the focal points of recent research on the behavior of new blended cement matrices in aggressive environments. The material selected for this study was ceramic waste (CW) rejected by Spanish manufacturers, primarily for reasons such as unsuitable kiln temperature or dimensional or mechanical failure. The resistance of CW‐containing cement pastes to three aggressive environments (SO₄^2?, Cl^?, and substitute seawater) was tested using the Koch–Steinegger method in this in‐depth analysis of the effect of CW on the chemical resistance of new blended matrices. The samples were also tested for performance in freeze–thaw cycles. The reaction mechanism was analyzed using X‐ray diffraction (XRD), pore‐size distribution, scanning electron microscopy (SEM), and backscattered electron images (BSE) with energy‐dispersive X‐ray (EDX) techniques. The results showed that CW contributed to cement resistance to such media; this enhancement of its mechanical properties was the result of the pozzolanic reaction induced by the addition of CW.     

Durability of traditional plasters with respect to blast furnace slag-based plaster

Blast furnace slag is a residue of steel production. It is a latent hydraulic binder and is normally used to improve the durability of concrete and mortars. Slag could be also used as rendering mortar for masonry and old buildings. Today, cement and hydraulic lime are the most popular hydraulic binders used to make plasters. They are characterised by a low durability when exposed to the action of chemical and physical agents.The aim of this study was to provide a comparison between the physical-mechanical properties of some renders made with ordinary Portland cement, hydraulic lime, or slag. Furthermore, an investigation was carried out to analyse mortar resistance to several aggressive conditions like acid attack, freezing and thawing cycles, abrasion, sulphate aggression, cycles in ultraviolet screening device, and salt diffusion. The specimens, after chemical attack, have been characterised from the chemical-physical [specific surface according to the BET (Brunauer-Emmet-Teller) method], crystal-chemical (X-ray diffraction, XRD), and morphological (scanning electron microscopy, SEM) points of view.     

The effect of SCMs and curing time on resistance of mortars subjected to organic acids

Agricultural effluents such as liquid manure and ensilage effluents contain organic acids that constitute a severe chemical threat toward the concrete of agricultural structures. In contact with an acidic solution, the chemical equilibrium of the hydrates in cement paste is destabilized, causing negative effects on porosity, reinforcement corrosion, mechanical strength, and, in the long term, may result in the collapse of the structure. More durable concrete in this environment is needed. The purpose of this study is to examine the effect of the nature of the supplementary cementing materials (SCMs) as well as the curing time on the chemical and the physical modifications of cement pastes and on the compressive strength, mass loss, altered depth and microstructure of mortars immersed in acetic acid at a pH of 4.This study concentrated on three types of hardened cement pastes or mortars made with ordinary Portland cement (OPC), slag and metakaolin cements, cured for period varying from 28 days to 1 year. The results show the beneficial effect of the curing time before the acid immersion, the better durability of metakaolin cement and the good chemical resistance of the slag cement against acid attack. The latter develops low compressive strength and is more sensitive to the curing time but the drop of its resistance due to the acid immersion is minimal due to its strong chemical resistance.     

Studies on chemical resistance of low water/cement ratio concretes

Solutions containing mineral acids, and certain organic acids and salts are highly corrosive to portland cement concrete. Since permeability is the key factor governing the rate of deterioration, it is customary to use a low water-cement ratio in making concretes or concrete overlays required to resist corrosive action of aggressive chemical solutions. Pozzolanic admixtures are often used to provide additional protection against acidic attack. Highly reactive pozzolanic admixtures, such as condensed silica fume, which rapidly react with calcium hydroxide and reduce both the alkalinity and permeability of concrete are now being used for improving durability. During the last two decades, latex admixtures have also found widespread application. The polymeric constituents of a latex seem to coat the alkaline hydration products of portland cement, thus protecting them from attack by aggressive solutions.

An experimental study was undertaken to evaluate the relative chemical resistance of low water-cement ratio concretes, containing either a styrene-butadiene latex or a silica fume admixture, to the following solutions; 1% HCl, 1% H₂SO₄, 1% lactic acid, 5% acetic acid, 5% ammonium sulfate, and 5% sodium sulfate. Time taken to register 25 percent weight loss by fully submerged concrete specimens was used as a criterion for failure. From the data it appears that, except for the ammonium sulfate solution, the concrete containing the silica fume generally showed better resistance to chemical attack than other concrete types.     

Potential use of natural perlite powder as a pozzolanic mineral admixture in Portland cement

This paper investigates the effect of incorporating natural perlite powder (NPP) as a cement replacement on cementitious materials properties. For this purpose, cement pastes and mortars were prepared by replacing 5, 10, 15, and 20% of NPP by mass of the Portland cement. Physicomechanical performances of pastes and mortars based NPP were inspected using normal consistency, setting times, heat of hydration, and compressive strength testing. Resistance against sodium sulfate attack and sulfuric acid attack were also assessed to investigate the durability characteristics of different mortar mixes. Experimental results show that cement pastes and mortars incorporating up to 20% of NPP demonstrate satisfactory physical and mechanical properties with very comparable results to cementitious materials without NPP. In addition, improved sulfate and acid attacks resistance with increased NPP content were demonstrated. The X-ray diffraction analyses confirm that NPP can be considered as a good pozzolanic material that can be used satisfactorily as a mineral admixture in cement production.     

Microstructural characterization of leaching effects in cement pastes due to neutralisation of their alkaline nature: Part I: Portland cement pastes

When concrete is exposed to the elements, its underlying microstructure can be attacked by a variety of aggressive agents; for example, rainwater and groundwater. The knowledge of concrete resistance to long term water aggression is necessary for predictions of their performance in different environments. This study aims to analyse the effects of leaching on the microstructure of Portland cement binders. Leaching of cement pastes was performed by an accelerated extraction leaching test that produces significant degradation and helps to achieve equilibrium or near-equilibrium conditions between the leachant medium and cement paste. FTIR spectroscopy, TG-DTA thermal analysis, low temperature nitrogen gas sorption, and geochemical modelling were used to characterize the microstructural changes produced in cement pastes at different equilibrium pHs reached during the leaching process.     

Evidences of chemical interaction between EVA and hydrating Portland cement

In spite of the widespread use of ethylene/vinyl acetate copolymer (EVA) in mortar and concrete production, there is no agreement among various researchers about the kind of interaction that is developed between cement and polymeric phases. Therefore, the adoption of adequate measures for final product quality achievement is impaired, as well as the adjustment of their properties to the desired performance. The purpose of this research is to fill this lack of knowledge through the microstructural characterization of cement pastes modified with EVA copolymer. Portland cement pastes were prepared with different EVA contents. The water/cement ratio was kept constant. The pastes were submitted to two different curing conditions, and analyzed at 28 days old. Thermal analyses (differential thermal analysis [DTA] and thermogravimetric [TG] analysis), Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) tests were performed, which permitted the evaluation of the EVA effects on the cement hydration. Some evidences of chemical interactions between cementitious and polymeric phases were identified. The results showed that the acetate groups of EVA copolymer undergo alkaline hydrolysis and interact with Ca²⁺ ions of the pastes to form an organic salt (calcium acetate). The calcium hydroxide content is decreased, the ettringite crystals appear to be well formed and many Hadley's grains were observed. A calcium-rich, porous and hexagonal structure phase was detected, probably due to acetic acid attack on calcium hydroxide crystals.     

Hydration and durability of sulphate-resisting and slag cement blends in Caron's Lake water

The problem of aggressive attack of sulphate and chloride ions has been of considerable scientific and technological interest because this attack is one of the factors responsible for damage to concrete. The corrosive action of chlorides is due to the formation of chloroaluminate hydrates, which causes softening of concrete. Sulphate ions can enter into chemical reactions with certain constituents of concrete, producing sulphoaluminate hydrates and gypsum, which cause the expansion of concrete. The aim of the present work is to study the hydration and the durability of mixed cement (sulphate-resisting and slag cement blends) pastes and mortars in Caron's Lake water. Different mixes of sulphate-resisting cement (SRC) with various proportions of slag cement were prepared and immersed in tap water for 3, 7, 28 and 90 days. The durability of the cement mortars was followed by curing the samples in tap water for 28 days (zero time) then immersed in Caron's Lake water for 1, 3, 6, 9 and 12 months. The hydration behavior was measured by the determination of the compressive strength, free lime, evaporable and nonevaporable water, total chloride and total sulphate contents at each curing time. The increase of substitution of SRC with blast-furnace slag cement (BFSC) up to 30% increases slightly the total pore volume. The free lime contents decrease sharply in the first months of immersion then slightly up to 1 year. The blended cement pastes made of SRC with BFSC up to 30 mass% have lower values of total chloride and total sulphate, while the mortars containing only SRC have lower values of compressive strength than those of all blended cement mortars at all curing ages of immersion under Caron's Lake water. Useful conclusions and recommendations concerning the use of 70 mass% of SRC with 30 mass% slag cement produces a highly durable mixed cement.     

低品位粉煤灰的改性及其对水泥浆体强度和自收缩的影响

采用石灰石粉对低品位粉煤灰进行煅烧改性,利用X射线衍射、扫描电镜和能谱分析等方法对改性粉煤灰的矿物组成和化学组成进行表征.同时测定了掺改性粉煤灰的水泥浆体的抗压强度和自收缩,并采用背散射扫描电镜和压汞测孔仪研究了掺改性粉煤灰水泥浆体的微观结构.结果表明,粉煤灰经煅烧改性生成了水硬性矿物β-C2S,水化可生成CSH凝胶,改善了等外粉煤灰颗粒与水泥基体的界面粘接,降低了复合水泥浆体的孔隙率和自收缩,提高了复合水泥浆体的强度.     

阿利特-硫铝酸钡钙水泥抗硫酸盐侵蚀性能的研究

本文研究了石膏掺量对阿利特-硫铝酸钡钙水泥抗硫酸盐侵蚀性能的影响,并与硅酸盐水泥进行了比较;利用XRD,SEM-EDS等测试方法对侵蚀后水泥水化产物的物相组成和形貌进行了分析.研究结果表明:阿利特-硫铝酸钡钙水泥具有良好的抗硫酸盐侵蚀性能.当石膏掺量为5%时,阿利特-硫铝酸钡钙水泥的抗蚀系数达1.31,而硅酸盐水泥的抗蚀系数仅为0.94.石膏对阿利特-硫铝酸钡钙水泥硬化浆体的致密性有较大影响,进而影响水泥的抗硫酸盐侵蚀性能.同时,对阿利特-硫铝酸钡钙水泥的抗侵蚀机理进行了初步分析.     

Physicochemical equilibria of cement-based materials in aggressive environments—experiment and modeling

Assessment of the integrity of concrete structures during their service life begins by considering the durability of the material in its environment. Experiments have clearly improved the understanding of the degradation mechanisms of concrete, mortars, and cement pastes under various aggressive environments. As far as radioactive waste containers are concerned, leaching by water has to be considered. Leaching experiments of cement pastes by aggressive solutions are shown to result in degradations with different kinetics. Three cement pastes with variable water-to-cement (w/c) ratio (0.25, 0.4, and 0.5) in two solutions (pure water and mineralized water) were investigated by TG/DTA, SEM-EDS, and by application of the NIST (National Institute of Standards and Technology) microstructure models. Leaching kinetics, evolution of the solid skeleton, and pore solution were experimentally studied and successfully modeled, using a reactive-transport approach. The discrepancies between modeling and experimental results highlight the understanding of complex degradation mechanisms. New results on the interactions on the aggressive solution and the cementitious material, through the pore solution, are presented.     

Degradation of cement-based materials by various organic acids in agro-industrial waste-waters

The paper analyses the mechanisms of the degradation of cementitious materials by three organic acids: oxalic, citric and tartaric acids, and evaluates their relative aggressiveness compared to that of acetic acid. These acids have different chemical characteristics in terms of poly-acidity and chemical and physical properties of their calcium salts. The aim was to highlight the links between these properties and the aggressiveness of each acid toward concrete. Degradation mechanisms and kinetics were investigated (using EPMA, XRD and SEM) on cement paste specimens immersed in acid solutions for one year.The results showed that oxalic acid was not aggressive to the matrix. Citric acid caused the highest kinetics and severe degradations in the paste. Tartaric acid attack developed in two stages: no visible degradation was observed in the first weeks and then damage occurred, the kinetics remaining moderate. Acetic acid had intermediate aggressiveness.It was confirmed that the solubility of the calcium salts was a major parameter of aggressiveness. It also appeared that, even if salts precipitated, they were not necessarily protective, the protection being correlated with the salt's molar volume. Moreover, poly-acidity seemed, in some cases, to increase the aggressiveness of the acid.     

Accelerated tests of hardened cement pastes alteration by organic acids: analysis of the pH effect

Effluents, such as liquid manure and silage effluents, stored in silos often made of concrete, contain organic acids that are chemically very aggressive for the cement-based matrix. The pH of liquid manure is comprised between 6 and 8, and the pH of silage effluent is about 4.There has already been much research done on manure's effect on concrete using aggressive solutions with a pH of or inferior to 4, in order to accelerate alteration kinetics. These studies aimed at simulating liquid manure and silage effluent, equally.The goal of this article is to validate the use of solutions with a pH of 4 to implement accelerated studies on alterations occurring to structures exposed to the acidic part of liquid manure.In this study, the alteration mechanisms of the cement-based matrix produced by two solutions of organic acids with pH of 4 and 6 were compared.At the end of the experiment, carried out on ordinary Portland cement and slag cement pastes, the kinetics of alteration of the cement pastes immersed in the solution with a pH of 4 was ninefold higher than in the solution with a pH of 6.The chemical and mineralogical modifications of the paste were analyzed by electron microprobe, XRD and BSE mode observations.It was shown that the alteration mechanisms of the paste are sensibly identical for both solutions: almost complete decalcification, the disappearance of the crystallized or amorphous hydrated phases and the probable formation of a silica gel containing aluminum and iron, mainly. The differences in alteration mechanisms between the two solutions are minor and mainly concern the stability of the anhydrous phases: C₄AF and slag grains.     

The influences of siliceous waste on blended cement properties

The influences of siliceous waste on the properties of fly ash and blast furnace slag cement were studied, and its optimum mixing amount in blended cement was determined. The strength, setting time, resistance to chemical attack, dry shrinkage, and impermeability of blended cement mixed with siliceous waste were also investigated by different experiments. The measurement of pore size distribution for hardened cement pastes made by Poremaster-60 was recorded and analyzed in this article.     

Effect of magnesium and sulfate ions on durability of silica fume blended mixes exposed to the seawater tidal zone

The effect of silica fume on deterioration resistance to sulfate attack in seawater within tidal zone and simulated wetting-drying condition has been studied in Portland cement concretes and pastes containing silica fume (SF) with/without ground granulated blast furnace slag (GGBS). Changes in the compressive strength and capillary water absorption of specimens as a function of SF content have been investigated combined with phases determination by means of scanning electron microscopy and X-ray energy dispersion analysis. The strength change factors (SCFs) of specimens with SF (the more SF content, the higher strength loss) were greater than that of the mixes without SF or cured under tap water. Mg²⁺ ion originated attack found to be the dominating deterioration mechanism as confirmed by X-ray and chemical analyses.Further, the incorporation of GGBS with SF mixes in different exposure conditions led to the worst performance in all of the test environments. Lower cement content and hydration rate accompanied with particular chemical composition of GGBS made concrete and paste specimens to be more susceptible to deleterious seawater environment.     

Limitations of Köch-Steinegger test to evaluate the durability of cement pastes in acid medium

The durability of ordinary Portland cement and ground granulated blast furnace slag pastes in buffered acetic/acetate medium (pH 4.5) was studied by means of the Köch-Steinegger test. Results show that flexural strength measurement is not a good parameter to evaluate the degradation degree of cement paste in acid medium because two effects take place with opposite consequences on flexural strength as a result of acid attack: a densification of the cement paste in the specimen core and a degradation of the outer surface with loss of resistance.     

硫酸盐侵蚀下硬化水泥浆体微结构演变及膨胀过程的数值模拟

根据硫酸盐侵蚀机理,利用改进的CEMHYD3D水化模型和随机概率方法,建立了硫酸盐侵蚀下硬化水泥浆体的微结构演变模型。在微观层次上,模拟了浆体孔溶液中硫酸根离子的自由扩散、随机碰撞和转化反应,分析了膨胀性侵蚀产物生长导致的微结构损伤和体积膨胀,计算了侵蚀过程中石膏和钙矾石的生成量及浆体的膨胀应变,并与已有试验结果对比分析验证了模型的合理性。在此基础上,数值模拟了硫酸盐侵蚀下不同水灰比水泥浆体的微结构演变及膨胀过程。结果表明：同一硫酸盐浓度下,硬化水泥浆体中氢氧化钙和含铝物相与孔隙的接触面积越小,浆体的膨胀应变越低;水灰比为0.25、0.30和0.35的硬化水泥浆体的孔隙填充程度分别达到9.09%、9.27%和9.41%时,浆体膨胀应变开始快速增大;硫酸盐侵蚀溶液浓度增大,浆体体积快速膨胀的时间提前。