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The use of high percentages of substitution of Portland cement by pozzolans can provoke the total consumption of portlandite. The present research proposes the study of ternary systems of Portland cement (PC), fly ash (FA), and hydrated lime (CH). After 180 days of curing, the mortar with 50% substitution of PC by FA obtained 65.9 MPa versus the mortars with an addition of 20% of CH and control mortar (100 PC) that obtained 69.9 MPa and 76.7 MPa respectively: this behavior is very positive value considering that tested FA containing mortars had a 50% of Portland cement. Regarding the effect of the amount of extra hydrated lime on durability issues, the evolution against carbonation of PC-FA and PC-CH-FA mortars was studied: the reduction of carbonation velocity was around a 37% for the mortar with CH respect the PC-FA mortar., El uso de altos porcentajes de sustitución de cemento Portland por puzolanas puede provocar el consumo total de la portlandita. La investigación propone el uso de un sistema ternario formado por cemento Portland (PC), ceniza volante (FA) y cal hidratada (CH). Después de 180 días de curado, el mortero con un 50% de sustitución de PC por FA obtiene 65.9 MPa de resistencia frente a los morteros con un 20% de CH y control (100 PC) que obtuvieron 69.9 MPa y 76.7 MPa respectivamente; este comportamiento es muy positivo teniendo en cuenta que este mortero tiene un 50% menos de PC. El efecto de añadir la cantidad extra de cal hidratada tiene efectos en la durabilidad; se estudió la evolución de la carbonatación de los morteros con PC-FA y PC-CH-FA. La reducción de la velocidad de carbonatación fue del 37% para los morteros con CH respecto al mortero con PC-FA.

Mineral carbonation of construction and demolition waste is a viable alternative for the reduction of CO2 emissions from industry. Concrete and cement, together with ceramic blocks, are the primary sources of calcium for mineral carbonation in which CO2 is fixed in a stable and inert process. One type of concrete was selected from 5 for the carbonation tests. Crushed, separated into size fractions, moistened to 20% and tested at 10 bars of CO2 for 24 to 720 h. Destruction of portlandite and ettringite phases was determined. Calcite precipitated as carbonate phase. Maximum carbonation was reached after 72 h, fixing 6.5% of CO2.

Solidification/stabilization (S/S) has been widely used for effective treatment of dredged sediment (DS) for many years, with the objective of improving the mechanical properties of DS through the addition of inorganic cementitious materials. Most previous studies have reported the short-term performance of S/S. However, long-term effectiveness is critical, as contaminants remain underground and are subjected to a variety of environmental stresses that can degrade S/S materials. In this regard, this experimental work investigated the long-term efficacy of solidification/stabilization of dredged contaminated sediments (DCS) treated with a new integrated method, namely PHDVPSS, which uses a prefabricated horizontal drain (PHD) assisted by vacuum pressure (VP) as well as solidification/stabilization. The DCS were treated with Portland cement (PC) as binder in the PHDVPSS method (abbreviated as VP-PC) at different zinc (Zn) concentration levels and compared with the traditional cement-based solidification/stabilization method (abbreviated as SS-PC). A series of experimental tests such as unconfined compressive strength (UCS), toxicity characteristics leaching procedure (TCLP), X-ray diffraction (XRD) and scanning electron microscopy in conjunction with energy-dispersive spectroscopy (SEM–EDS) were performed to assess the long-term strength, leaching and microstructural characteristics of high-water-content DCS, respectively. The UCS test results indicated that the strength of VP-PC mixes increased significantly with curing time compared to the limited strength development of SS-PC mixes. After 180-day curing, VP-PC mixes exhibited 3.5–5.5 times higher UCS values than the SS-PC mixes. Furthermore, when compared to the SS-PC mixes, the VP-PC mixes had 14.7–36.4% lower leached Zn concentrations at different Zn levels. This is attributed to an increase in the least reactive F4 (residual) fraction and a decrease in the most mobile F1 (acid-soluble) fraction as confirmed by the BCR method. Microstructural tests including XRD and SEM–EDS revealed that calcium silicate hydrate–like compounds were identified as the main hydration products of both the VP-PC and SS-PC mixes. However, portlandite, a major hydration product of PC, was not detected in either case, which is attributed to the retardant effect of Zn on cement hydration. Overall, the experimental results showed that the PHDVPSS method, when compared to the conventional solidification/stabilization method, is a viable choice for treating high-water-content DCS at different Zn concentration levels with low cement content.

Our study focuses on the characterization of sludge from the sewage treatment plant located in Mila (Algeria) for the target to use it as fertilizer in agriculture or as a useful material for manufacturing cement and refractory materials. The reuse of sludge in building materials not only minimizes the drain problem, but also has an economic and ecological advantage. So that a several analyses were carried out using: XRF, XRD, FTIR, TG-DSC, COD, pH, NO3− and TOC. Analysis of X-ray fluorescence spectrometry indicates the presence of fertilizer elements such as K, P, S and Mg. A large percentage of the following elements: Fe, Ca, Si and Al as well is present. The studied sludge also contains trace metals. The mainly existing elements are the following: Cu, Cr, Zn, Ni and Pb with contents smaller than the maximum values admitted by the Algerian standard NA 17671. However, the Zn and Ni concentrations represent 85% and 75%, respectively, of the standard values. So Zn and Ni are factors that can create risks during their agricultural spreading. The measurement of the concentration of dissolved nitrate ions and the COD gave us the values of 2.4518 mg/g and 1.4 mg/g, respectively. The rate of organic matter is estimated at 48.5%. The measured pH is in vicinity to neutrality. The spectral study of the XRD and the IR indicate the presence of the important phases such as calcite, quartz, portlandite and sillimanite in the studied sludge. The results of the TG-DSC thermogravimetric analysis are very encouraging. According to the TG-DSC curve, the decarbonation takes place between 700 and 1000 °C, and it finishes with the release of lime in a particularly reactive state. The final combinations between the obtained lime are SiO2, Al2O3 and Fe2O3 which yielded a very interesting mineral in the construction field, which are the four main minerals in clinker Ca3SiO5; Ca2SiO4; Ca3Al2O6 and Ca4Al2Fe2O10.

This article presents an investigation into the effects of lignocellulose nanofibrils (LCNF) and delignified cellulose nanofibrils (DCNF) on the hydration, microstructure, and mechanical properties of cement paste. The effects of various fine contents and dosages of the cellulose nanofibrils (CNF) additions on the properties of cement paste are presented in this article. Nearly all the CNF containing batches were observed to have an accelerated cement hydration reaction within the first 30 h. However, after 80 h of hydration, the CNF additions no longer exhibited any significant effect on the degree of hydration. The cement paste batches with LCNF were observed to have improved workability compared to those with DCNF. It was further observed that the compressive and flexural strengths of the cement paste can be increased up to 20% and 111%, respectively, by the addition of CNF. Both LCNF and DCNF were found to reduce the amounts of ettringite and portlandite in the hydrated cement paste. The ideal fine content of CNF to achieve both microstructural and mechanical performance enhancement was observed to be around 75%. The experimental findings presented in this article indicate that LCNFs with low fine content (60–75%) would be a more desirable and potentially more economical additive for concrete production compared to the DCNFs with high fine contents.

Development of sustainable materials has become one common goal across the globe to meet the ever-increasing demand for the construction materials. High volume fly ash (HVFA) concrete is one such sustainable construction material which utilizes fly ash in concrete as a partial replacement of cement. Though the existing literature focuses abundantly on high volume fly ash concrete, the present work aimed to explore the intricate hydration process thorough a systematic experimental program. A series of experiments including compressive strength, rapid chloride permeability, UPV, acid resistance, X-ray diffraction, SEM and EDAX were performed to examine the effect of varying proportions of fly ash (0%, 20%, 40%, 60%) on cement replacement. Analysis of results indicated formation of hydration compounds in the form of alite, belite, celite, portlandite and tobermorite (C-S-H gel). Results of mechanical and durability tests showed that, to achieve maximum benefits, cement can be replaced to an optimum value of fly ash of 40%. The authors believe that the formation of hydration compounds tobermorite and celite resulted in attaining enhanced durability and strength in high volume fly ash concrete.

This experimental study reports the weighted fraction of hydrated products of cement-based foam and examines their influence on pozzolans and thermal conductivity. These hydrated products were formed as the result of hydration in the cement-based foam mixtures prepared by substituting cement with fly ash, silica fume, and metakaolin, up to 20% by weight in the binder. To monitor the maturity of the hydration products, three different hydration periods, namely 60th, 120th, and 210th day, were selected. X-ray diffraction technique was used here for the identification of phase spectrums while the Rietveld quantitative X-ray diffraction method was employed for the quantification of the weighted fraction of hydrated products. The weighted fraction results showed that the consumption of portlandite (CH) increases with the inclusion of pozzolan and the higher substitution ratio further increases this consumption. In addition, the results reveal that the portlandite (CH) and calcium silicate hydrate (CSH) govern the thermal conductivity of cement-based foam mixture including those blended with pozzolan.

Assessing the potential uses as industrial mineral, bauxite from Debele, Guinea, has been characterised by chemical and mineralogical analyses, the determination of the amorphous content, the rate of portlandite consumption in an aqueous solution, the strength activity index, and the thermal behaviour up to 1200°C. It was evidenced that the raw sample is gibbsite-rich type bauxite with about 45.06 wt% of alumina, 23.80 wt% of iron oxide, and 1.74 wt% of silica. It meets the chemical composition required for bauxites used for refractory cement. During heating, the raw bauxite undergoes high densification with low linear shrinkage, motivating a potential use in dense ceramic compositions with high thermal stability. Also, the heating at only 600°C gives a significant pozzolanic activity in combination with Portland cement. The correlation between the pozzolanicity, the amorphous phase content, and the specific surface area indicated that the raw and the calcined materials present an interesting reactivity for using them in alternative cement formulations.

Spectroscopy is the interaction between matter and electromagnetic radiation, which is useful in the determination and characterisation of various chemical composition existing in the material. Present paper, focuses on predicting the extent of thermal damage on hydrated Portland Cements (PC), using Fourier Transform Infrared Spectroscopy (FTIR). The hydrated specimens of Portland Pozzolana Cement (PPC) and Ordinary Portland Cement (OPC), were subjected to temperatures ranging from 27 °C − 800 °C, for an interval of every 100 °C was analysed. Variation in the absorbance peaks obtained from FTIR, is correlated with the Thermal analysis (TA). At temperatures beyond 400 °C, reduction in the absorbance values at wavenumbers of 3430 – 3440 cm−1 of Ettringite phase for PPC and OPC specimens was observed. However, in OPC specimens, an increase in the absorbance values of Portlandite phase at wavenumbers ranging from 3640 to 3645 cm−1 was observed. The phase changes taking place in the PC specimens observed using FTIR, are in good agreement with the mass loss and heat flow plots obtained from TA. Therefore, it can be concluded that FTIR analysis is suitable test method in predicting the thermal damage of concrete specimen.

The current study was focused to find the impact of the dissolution of Ground Granulated Blast Furnace Slag (GGBS) in water before combining it with the other proportions of mortar. Two mixing types were used in the study. First, the conventional mixing method, wherein the GGBS was added with the cement and sand. Second, the new mixing method, wherein the GGBS was dissolved in water before adding to cement and sand. Five dissolution times (0, 1, 3, 6, 12 h) were studied with various percentages of GGBS as cement replacement (0%, 2.5%, 5%, 10%, 20%).The new mixing method has given higher compressive strength as compared to the conventional mixing method. The maximum compressive strength was obtained at 2.5% and 5.0% GGBS for a standing duration of 1 hr immersion in water. The higher compressive strength of mortar cubes was due to the hydrolysis of GGBS in water and was determined by the mobility of Ca and Si ions. As the ratio of Ca/Si decreased, the compressive strength was increased and was more prominent as long as the portlandite Ca(OH)2 was in active state. The compressive strength at earlier stage was developed because of the pozzolanic activity and mobility of ions.

ZSM-5 waste, the spent product of ZSM-5, has a high content of active SiO2, and thus, it can be potentially used as a supplementary cementitious material (SCM) in cement. In this paper, standard mortars with 5, 7, and 10% of cement replacement were prepared, and the compressive strength and fluidity were tested. The characterization techniques included: X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), hydration heat liberation, and Thermal gravimetric (TG). Results demonstrate that the addition of ZSM-5 waste can improve the strength, decrease the fluidity of cement mortar, and reduce the hydration heat of cement. Cement paste with the addition of ZSM-5 waste shows a lower amount of portlandite due to the pozzolanic reaction. Besides, the microstructure of reaction products exhibits a more condensed structure.

This study investigated the influence of aggressive acid and sulfate media on the phase transformation of cement materials to which natural rubber latex was added. After 28 days of curing underwater, all samples were subjected to sulfuric acid (H2SO4) and sodium sulfate (Na2SO4) solutions for 0, 7, 14, or 28 days. After that, X-ray diffraction (XRD) was used for phase identification. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was used to confirm the chemical functionally of the samples. The microstructure and elemental composition were also studied using scanning electron microscopy (SEM) and energy X-ray dispersive spectroscopy (EDS), respectively. XRD data showed no evidence of any clear relationship in rubber-modified cement pastes between any phase transformation and natural rubber content. FTIR results confirm the presence of portlandite, calcite, gypsum and C–S–H phases and indicate interaction between the rubber and cement phases. The inclusion of natural rubber latex in cement led to formation of a water channel structure of the bassanite phase (CaSO4 0.625H2O) after 14 and 28 days of exposure to sulfuric acid solutions. Bassanite (CaSO4 0.5H2O) and the water channel structures of bassanite were not found in the samples after sodium sulfate attack. Based on the results of compressive strength tests, it was suggested that an optimal ratio (rubber/cement = 11.11%) enhanced the stability of cement paste after acid and sulfate exposure. From SEM images, a major change in morphology was observed for samples exposed to H2SO4 compared to those subjected to Na2SO4.

Cement-based materials (CBMs), such as paste, mortar and concrete, are highly alkaline with an initial high pH of approximately 12.0 to 13.8. CBMs have a high pH due to the existing oxide mineral portlandite and alkali metal contents in Portland cement. The high pH of concrete provides excellent protection and reinforces the steel bars against corrosion. The pH of concrete does not remain constant due to ageing and other defect-causing factors, such as chloride ingress, alkali leaching, carbonation, corrosion, acid attack, moisture and biodegradation process. Reducing the concrete pH has negative impact on the strength, durability and service life of concrete buildings. However, the high pH of concrete may also cause concrete structure deterioration, such as alkali silica reaction, porosity and moisture related damages in concrete structures. The pH of CBMs can be influenced by high temperatures. For instance, the extremely high volume (85%–100%) of slag-blended cement pastes shows considerable pH reduction from 12.80 to 11.34 at 800 °C. As many concrete structure deterioration are related to concrete pH, using an accurate and reliable method to measure pH and analyse the durability of reinforced concrete structure based on pH values is extremely important. This study is a comprehensive review of the pH of CBM in terms of measurement, limitations and varying values for different CBM types.

This work deals with the comparison of micromechanical properties and microstructure of cement pastes with additives used in concrete to reduce the lateral pressure on the formwork. This work is a steppingstone for broader investigation of the lateral pressures on different cement mixtures. The work focused on two additives used for the purpose, namely calcined clay (metakaolin) and a type of nanoclay sepiolite. A scanning electron microscope was used to describe their microstructure. Micromechanical properties of both cement composites were investigated by nanoindentation. Large statistical grids of indents were performed on three sample types: plain cement paste and two mixtures containing the enhancing additive of metakaolin and nanoclay. From the evaluated results in the form of property histograms, the modulus of elasticity, hardness and creep parameter were derived. It was found that in the cement paste with metakaolin the amount of C-S-H gel increased compared to the control mixture. Increased portlandite and the amount of unhydrous clinker was found in the cement paste with nanoclay. Nanomechanical response of individual phases was derived from overall property histograms by statistical deconvolution. The results were confirmed by electron microscopy. The micromechanical research was supplemented with the measurement of the compressive strength on cubes at the macroscopic level.

This study investigated the compressive strengths and leaching of heavy metals in high-volume fly ash cement (HVFAC) pastes with and without nano-SiO2 (NS). Further, scanning electron microscopy, X-ray diffraction, and mercury intrusion porosimetry were used to characterize the microstructure of the specimens. The results showed that the addition of NS increased the compressive strength of HVFAC specimens. NS accelerated the hydration of both cement and fly ash to form more hydration products, and it reacted with portlandite to simultaneously generate more C-S-H gel. Thus, the total pore volume, especially the capillary pores, in the NS-mixed HVFAC specimens was reduced, and their microstructure became denser because of the filling of more hydration products in the pores. This resulted in the reduction of the leaching of heavy metals (Cr, Pb, Cd, As, Zn, and Cu) in the NS-mixed HVFAC specimens compared with the HVFAC specimen containing no NS. According to the Chinese national standard (GB 3838–2002), the water quality of leachates from the HVFAC specimens mixed with both 3% and 5% NS reached grade I, thus causing nearly no harm to the water and soil environment.

The hydration process of Portland cement triggers reactions of stabilization of minerals from the contact of the clinker with water, which is the Hydrated Calcium Silicate (C-S-H), the Etringite (3CaO.Al2O3.3CaSO4.32H2O) and the Portlandite (Ca(OH)2). In order to understand the effects of the evolution of hydration in cement, it is possible to apply non-destructive tests. In this context, the objective of this work is to evaluate the influence of the type of cement, the curing age, of the format and humidity of the test specimens of concrete in the ultrasonic pulse velocity (UPV). In order to do that, 36 cylindrical test specimens (10 x 20 cm) and 9 cubic ones with 25 cm of edges, with mix proportion of 1:2,7:3,2 (cement/sand/gravel), water/cement ratio of 0.58 and three types of Portland cement (CP II-Z-32, CP IV-32 RS and CP V-ARI) were molded. With data obtained it was possible to correlate the increase of concrete strength along time (at ages of 7, 14, 28, 70 and 91 days) with the increase of the ultrasonic pulse velocity. Besides, it was possible to prove the direct influence of the concrete moisture and of the degree of hydration in the UPV. The shape of the test specimen generally had no influence on the results, except in the case of cement CP V ARI. Resumo O processo de hidratação do cimento Portland desencadeia reações de estabilização de minerais provenientes do clínquer em contato com a água, que é o Silicato de Cálcio Hidratado (C-S-H), a Etringita (3CaO.Al2O3.3CaSO4.32H2O) e a Portlandita (Ca(OH)2). Para o entendimento do efeito da evolução destes processos de hidratação, é possível aplicar o uso de ensaios não destrutivos. O objetivo do presente trabalho é avaliar a influência do tipo de cimento, da idade de cura, do formato e da umidade dos corpos de prova de concreto na velocidade de pulso ultrassônico (VPU). Para tal, foram moldados 36 corpos de prova cilíndricos (10x20 cm) e 9 cúbicos com 25 cm de arestas, com traço 1:2,7:3,2 (cimento/areia/brita), relação água/cimento de 0,58, e três tipos de cimento Portland (CP II-Z-32, CP IV-32 RS e CP V-ARI). Com os dados obtidos foi possível correlacionar o aumento da resistência do concreto ao longo do tempo (nas idades de 7, 14, 28, 70 e 91 dias) com o aumento da velocidade de pulso ultrassônico. Além disso, foi possível comprovar a influência direta da umidade do concreto e do grau de hidratação na VPU. A forma do corpo de prova, de modo geral não apresentou influência nos resultados, com exceção do caso do cimento CP V ARI.

Portlandite, Ca(OH)2, is a primary product in cement hydration, on which some biases or misconceptions persist, such as portlandite has inferior mechanical properties because of its layered microst...

LED waste quartz sand (LEDWS), which is a prominent by product of the LED manufacturing process, may contaminate the environment because it comprises specific heavy metals (e.g., As and Cu), which are hazardous ingredients to the environment when disposed of improperly. Therefore, this study investigated the use of light-emitting diode (LED) waste quartz sand to partially replace Portland Type I cement (OPC) to evaluate the feasibility of reusing it as a pozzolanic material. The SiO2, Na2O, and CaO contents in the LED waste quartz sand were 70.37, 16.52, and 9.19%, respectively. The results showed that the LED waste quartz sand met the Taiwan EPA regulatory thresholds. Microstructure analysis techniques, such as mercury intrusion porosimetry (MIP), X-ray diffraction (XRD) and scanning electron microscopy (SEM), were used to measure the LED waste quartz sand-blended cement paste (LEDBCP) samples. Compressive strength analysis of the pastes containing 10 wt.% LED waste quartz sand showed that the LED waste quartz sand not only acts as a pozzolanic material to increase the density of the microstructure but also improves the compressive strength of the pastes. LEDBCP with LED waste quartz sand exhibited higher intensity diffraction peaks corresponding to calcium silicate hydrate and lower intensity diffraction peaks corresponding to portlandite (CH) compared with ordinary Portland cement samples at an early age. The gel porosity and pore sizes of the LEDBCP increased with increases in the proportion of LED waste quartz sand. LEDBCP with 10-20 wt.% LED waste quartz sand provides a paste with good pozzolanic characteristics.

Calcium-Silicate-Hydrate (C-S-H) has been studied extensively over the last few decades to gain understanding toward the underlying mechanism of different stages during cement hydration. The variable stoichiometry and nanocrystallinity of C-S-H makes it difficult to characterize experimentally. The second most abundant hydration product of cement is portlandite which has a simpler crystalline structure in comparison to C-S-H and has been used as a training/building system for future simulation of C-S-H bulk and surfaces. In this PhD project we are interested in a better fundamental understanding of the interaction of sulfate and secondary ions (Aluminium, Magnesium,...) with cementitious materials (e.g. portlandite and C-S-H). It has been shown that sulfate considerably affects the morphology of growing portlandite and C-S-H which will affect the physical properties of cement and concrete. A better fundamental understanding of this adsorption or incorporation into bulk structures will improve our understanding of the growth of C-S-H in the presence of such ions. In this project, utilizing molecular dynamics and metadynamics, we will systematically investigate the interaction of ions found in cement pore solutions with portlandite and C-S-H. For this purpose, we will use the Brick model recently developed in our group by Mohamed et al. (1) to create model structures for the C-S-H. We also have started to develop a new force field (ERICA FF1) which constitute different atom types needed for these simulations which are not included in previous cement force fields (Cement FF1 (2) and Cement FF2 (3)⁠.

Refereed/Peer-reviewed The effect of high temperature on the mechanical, durability, and microstructural properties of mortar containing alum sludge ash (ASA) was investigated in this paper. The ASA was derived from grinding and calcinating alum sludge, a typical by-product of the drinking water treatment processes. Four different mortar mixtures with ASA content at weight percentages of 0%, 10%, 20%, and 30% (as cement replacement) were exposed to high temperatures of 300 °C, 550 °C, and 800 °C, respectively. The experimental results showed that mortar samples containing up to 20% of cement replaced with ASA exhibited superior high-temperature resistance to the reference ones (without ASA), especially after exposure to 800 °C. The thermal analysis determined the portlandite consumption because of ASA pozzolanic reaction, and the x-ray diffraction pattern showed that the ASA reaction might contribute to the formation of aluminum-bearing phases with excellent refractoriness in the binder matrix. In addition, crack examination conducted by backscattered electron images evidenced that the ASA addition mitigated the binder paste degradation.

The aim of this work was to benchmark several binders by testing their capacity to resist external sulfate attack (ESA) under similar experimental conditions. Concrete samples were fabricated from seven different binders: two Portland cements, one blast furnace slag Portland cement, one super sulfated ground granulated blast furnace slag cement, one sodium carbonate alkali-activated slag cement, one metakaolin geopolymer and one calcium sulfoaluminate-belite cement. Mechanical strength measurements were used to characterize the concretes in the hardened state. Resistance to ESA was studied by measuring the longitudinal expansion of concretes submerged in a sulfate solution. In order to better understand the behavior of the binders in ESA, this study was completed by microstructural and mineralogical analyses carried out before and after attack by using Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS), X-ray diffraction and thermodynamic calculations. It was found that ordinary Portland cement had high expansions (> 0.1%) due to the formation of excess ettringite caused by the reaction between aluminates and sulfates. Portland cement without C3A presented lower expansions but gypsum was found to be responsible for cracking at later ages. Alternative binders had low expansions, in the range of 0.01–0.03%, explained by the absence of C3A and portlandite, in addition to the formation of ettringite during hydration (case of ettringite binders) and the absence of calcium (case of the geopolymer-based metakaolin).

The influence of superplasticizer and silica fume on cement hydration, structure formation, phase composition, and cement stone properties is investigated. It was found that using a polycarboxylate superplasticizer reduces the normal consistency of the cement paste and increases the cement stone strength at 28 days by 22%. Replacing cement with silica fume in the absence of a superplasticizer does not increase the cement stone strength, but it reduces the open capillary porosity of the cement stone by 7%. The combined use of silica fume and superplasticizer increases the cement stone strength by 27% and reduces open capillary pores volume by 17% compared to the control sample without admixtures. According to the X-ray phase analysis results, it was established that the use of polycarboxylate superplasticizer leads to a slowdown in the hydration processes of clinker minerals at 1 day. The use of silica fume accelerates the cement hydration in the early hardening stages and compensates for the plasticizing admixture slowing effect. At 28 days, in the cement stone with silica fume, a decrease in the portlandite content by 39% is observed. The combined use of superplasticizer and silica fume leads to the formation of a cement stone structure with increased content of amorphized low-basic hydrated calcium silicates by 22%, which significantly densifies and strengthens the cement stone structure.

Durability predictions of concrete structures are derived from experience-based requirements and descriptive exposure classes. To support durability predictions, a numerical model related to the carbonation resistance of concrete was developed. The model couples the rate of carbonation with the drying rate. This paper presents the accelerated carbonation and moisture transport experiments performed to calibrate and verify the numerical model. They were conducted on mortars with a water-cement ratio of either 0.6 or 0.5, incorporating either a novel cement CEM II/C (S-LL) (EnM group) or commercially available CEM II/A-S cement (RefM group). The carbonation rate was determined by visual assessment and thermogravimetric analysis (TGA). Moisture transport experiments, consisting of drying and resaturation, utilized the gravimetric method. Higher carbonation rates expressed in mm/day−0.5 were found in the EnM group than in the RefM group. However, the TGA showed that the initial portlandite (CH) content was lower in the EnM than in the RefM, which could explain the difference in carbonation rates. The resaturation experiments indicate an increase in the suction porosity in the carbonated specimens compared to the non-carbonated specimens. The study concludes that low clinker content causes lower resistance to carbonation, since less CH is available in the surface layers, thus, the carbonation front progresses more rapidly towards the core.

This study addresses the application of polyvinyl alcohol (PVA) fibers to improve the performance of lightweight cement composites with pozzolans. Blended cement mixes based on expanded glass granules were modified with PVA fibers (Type A: Ø40 µm, L = 8 mm and Type B: Ø200 µm, L = 12 mm). The following research methods were used to analyse the effect of the fibers on the structure of cement matrix and physical-mechanical properties of lightweight composite: SEM, XRD, DTG, calorimetry tests, and standard test methods of physical and mechanical properties. Results from the tests showed that a denser layer of hydrates was formed around the PVA fiber and the amounts of portlandite, CSH, and CASH formed in the specimens with PVA were found to be higher. PVA fibers of Type A accelerated hydration of the cement paste, slightly increased the compressive strength of the lightweight composite, but had no significant effect on the values of density, ultrasonic pulse velocity and flexural strength. The shrinkage of cement composite was significantly reduced using both types of PVA fiber and both types of PVA fibers increased the fracture energy of lightweight cement composite with expanded granules.

Studies on recycling of deconstruction concrete into new concretes show that it is difficult to integrate fine recycled concrete aggregates in new concrete due to the high proportion of cement paste in the fine fraction which is porous and absorbs a lot of water. A way to upgrade this fraction is to use it in ground form as a main constituent of cement. Four types of fine recycled concrete aggregates were ground and added to an ordinary Portland cement type with a substitution rate of “25% wt%” in order to form Portland cement type CEM II/B. The mechanical strengths of the mortars with these composite cements were performed at 2, 7 and 28 days. The study shows that these ground fine aggregates do not act only as fillers but also have a binding property. This is due to their carbonate content which comes either from the natural aggregates used for the manufacture of concrete or from the carbonation of portlandite released during the cement hydration.

Geologic CO2 storage (GCS) is a method to mitigate the adverse impact of global climate change. Potential leakage of CO2 from fractured cement at the wellbore poses a risk to the feasibility of GCS. Foamed cement is widely applied in deepwater wells where fragile geologic formations cannot support the weight of conventional cement. Thus, it is critical to know whether fractures in foamed cement self-seal in a similar manner as conventional cement systems. This study is the first to investigate the changes in physical and chemical attributes of foamed cement under dynamic flow conditions using CO2-saturated water. Self-sealing of fractures in the cement was observed at a solution flow rate of 0.1 mL/min and a pressure of 6.9 MPa. The formation of CaCO3 precipitates in pore spaces and fractures led to a decrease in permeability by 1 order of magnitude. The extents of self-sealing in foamed cement samples, specifically the 20 and 30% air volume formulations, were similar to that of conventional cements. We attribute this to the greater alteration depth in the foamed cement, which compensated for the reduced availability of Portlandite and higher initial porosity. The results can be used to evaluate the risk of leakage associated with foamed cement.

This paper shows the results of a study focused on the evolution and properties of mortars made with a mixture of portland cement (PC) and natural mordenite (Mor). To begin, samples of mordenite, cement and sand were studied with X-ray diffraction (XRD), X-ray fluorescence (XRF) and granulometric analysis (GA). Next, mortars with a ratio of 75% PC and 25% mordenite were prepared to determine their initial and final setting times, consistency and density. Continuing, the density, weight and compressive strength of the specimens were determined at 2, 7, 28, 90 and 365 days. Finally, the specimens were studied using SEM, XRD and XRF. The results of the study of the mordenite sample showed a complex constitution where the major mineral component is mordenite, and to a lesser degree smectite (montmorillonite), halloysite, illite, mica, quartz, plagioclase and feldspar, in addition to altered volcanic glass. Tests with fresh cement/mordenite mortar (CMM) showed an initial setting time of 320 min and a final setting time of 420 min, much longer than the 212–310 min of portland cement mortar (PCM). It was established that the consistency of the cement/mordenite mortar (CMM) was greater than that of the PCM. The results of the density study showed that the CMM has a lower density than the PCM. On the other hand, the density of cement/mordenite specimens (CMS) was lower than that of portland cement specimens (PCS). The CMS compressive strength studies showed a significant increase from 18.2 MPa, at 2 days, to 72 MPa, at 365 days, with better strength than PCS at 28 and 365 days, respectively. XRD, XRF and SEM studies conducted on CMS showed a good development of primary and secondary tobermorite, the latter formed at the expense of portlandite, also, ettringite developed normally. This work proves that the partial replacement of PC by mordenite does not have a negative effect on the increase in the mechanical strength of CMS. It indicates that the presence of mordenite inhibits the spontaneous hydration of C3A and controls the anomalous formation of ettringite (Ett). All this, together with the mechanical strength reported, indicates that mordenite has a deep and positive influence on the evolution of the mortar setting and is an efficient pozzolan, meaning it can be used in the manufacture of mortars and highly resistant pozzolanic cement, with low hydration heat, low density, stability in extremely aggressive places and a low impact on the environment.

Carbon dioxide sequestration by cement-based materials is a chemical process known as carbonation. Carbon dioxide absorption by cement consists of its reaction with calcium hydroxide, among other Portland cement components. This phenomenon should be taken into account in the calculation of the net contribution of cement production to greenhouse gas emissions. Therefore, carbon dioxide uptake should be considered into future life-cycle assessment protocols. This paper presents the carbon dioxide absorption results recorded in paste specimens during almost four years by 15 different types of Portland composite cements made of siliceous coal fly ash, natural pozzolan, ground granulated blast-furnace slag and limestone. Prismatic (10 ​× ​10 ​× ​60 mm) Portland cement pastes made of several types of cement (5% and 35% by weight) and with two cement/water ratios (0.45 and 0.60) were manufactured. The specimens were cured at 95% relative humidity for 24+ ​48 ​h and afterwards they were kept under laboratory room conditions for 25 more days. After this period, a set of the specimens remained in the lab, whereas other were moved outdoors for being kept sheltered or exposed from rain. Thermogravimetric measurements were performed along the time to determine the carbon dioxide absorption by the Portland cement pastes. The results were fitted to an exponential function. The maximum carbon dioxide absorption and the absorption rate depends on the exposure conditions, the water/cement ratio, the cement type (calcium oxide contents, type and percentage of the additions in the cement paste and compressive strength) and portlandite formed at 28-days. The results of this paper show that the absorption amounts were 13% and 30% in weight. of ignited cement.

The presented study is a continuation of the research with the aim of finding a useful value of hazardous waste slag generated by the combustion of lignite in heating plants and its application in the construction industry. The different amounts of cement (10%, 15%, 20% and 25%) were replaced with waste slag and silica fumes in mortars and concrete production. Detailed physical–mechanical characterization was performed on the mortar and concrete samples according to standard procedures. Test results indicated that the replacement of cement with slag and silica fumes reduces the physical and mechanical properties of mortar and concrete, but cement composites retained the required structural properties. If 15–20% is considered an acceptable level of compressive strength decrease, then it can be concluded that waste slag can be implemented in practice and be used as a construction material, with cement replacement in the maximal amount of 20% (17.8% of slag and 2.2% of silica fumes). On hardened mortar samples with maximal possible cement replacement (20%), physical–chemical characterizations were performed and included X-ray and infrared spectrophotometry, scanning electron microscopy, and thermal analysis. Results showed the absence of new phases and the presence of only those which were characteristic for starting samples, predominantly portlandite, quartz, calcite and calcium silicate-oxide.

In numerous contexts, concrete can be exposed to chemically aggressive conditions that can damage their microstructure and reduce their lifespan. The concrete facilities from the agricultural and agro-food industries dedicated to the storage or the treatment of effluents are more particularly exposed to organic acids coming from the microbial activity naturally occurring in such media. This biodeterioration leads mainly to mineralogical transformations, such as hydrated and anhydrous phase dissolution, and to ion exchanges between acidic effluents and cement-based materials. The poorly crystalline mineralogy of hydrated cement pastes and their reactivity makes the geochemical behavior of such materials difficult to investigate and thus to predict over large periods of time and wide variety of chemical conditions. The degradation of cementitious materials in these aggressive conditions mainly leads to the leaching of calcium and the precipitation of amorphous secondary phases. The purpose of this work is (i) to assess the stability of the cement phases involved in such chemical conditions as well as to identify the alterations products, and (ii) to understand the evolution of concentration and the behavior of elements in solution such as aluminum or silicon. A thermodynamic model of cement pastes subjected to acid attacks has been developed, in order to reproduce, experimental data also presented here. Our model reproduces a major part of the behaviors shown by the experiments, i.e. a progressive decalcification of solid matrix (successive dissolution of portlandite, aluminates hydrates and C-S-H) during acid degradation and the identification of alteration zones in agreement with the experimental observations.

This paper focuses on the microstructural investigation of ultra-high performance concrete (UHPC) mixtures featuring various replacement levels for blast furnace slag (BFS), in the aim of becoming more environmentally-friendly. Three levels of slag are applied (namely 30%, 50% and 80%) per unit volume of cement. The microstructural characteristics examined included X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), and mercury intrusion porosimetry (MIP). These characteristics are assessed along with the mechanical strengths at 3 and 90 days. Similarly, the effects of chemical and thermal activation methods on incorporating BFS into UHPC mixtures at high volumes were studied from a microstructural point of view, and a comparison is drawn between the non-activated and activated mixtures. The results of this investigation show that the beneficial physical impact of slag replacement lies at the 30% level, due to its filler property in stimulating hydration to quickly generate portlandite. For this reason, the portlandite and C-S-H peaks are quite similar to those in the reference mixture (i.e. 0% BFS) at 3 and 90 days, as demonstrated in the XRD analysis. Moreover, the pore size distribution could be refined, the microstructure densified (as indicated on the TEM images), and compressive strengths at both ages improved. In contrast, for slag replacement levels of 50% and 80%, the portlandite and C-S-H peaks are significantly lowered, as observed in the XRD analysis, thus causing a magnification of the capillary pores and a drop in compressive strength at 3 and 90 days. Chemical activation through a potassium hydroxide, with a dosage of 10.17 kg/m3, at the 80% BFS replacement level is able to accelerate hydration and portlandite consumption, as exhibited in the XRD analysis through the absence of portlandite peaks and limited quantities of C-S-H at 3 and 90 days. However, this step results in smaller pores and a higher compressive strength. As for the thermal activation, the portlandite in the blended mixtures with 50% and 80% BFS replacement decreases in quantity, as confirmed by XRD analysis, and the reaction is perfectly activated by means of the solubility acceleration of the alkalis; consequently, the pore structure is compacted, as revealed on the TEM image and the compressive strength rises considerably.

An investigation is about the role of GO on the dissolution behaviours and hydration process of alite (Fe, F-C3S, abb. C3S) in a synthetic cement system, which also contains aluminate (Fe, F-C3A, abb. C3A) and gypsum. The results show that GO can increase the undersaturation levels of starting materials (C3S, C3A and gypsum) and thus promote their dissolution. The dissolution of C3A might be more sensitive than that of C3S due to the fluctuation of Ca concentration in pore solution before 30 min. Trace amount of GO could accelerate the interfacial dissolution rate of C3S throughout 24 h. As for the precipitation behaviours, GO could increase the supersaturation level of portlandite while decrease that of ettringite and C–S–H. In general, GO can improve the hydration degree of C3S by up to 15.0% and accelerate its hydration reaction rate by 33.6%. It is notable that the morphology changes of C–S–H from foil-like for reference to fibrous-like for GO-containing system at 2 h were likely attributed to the supersaturation of portlandite.

Bicarbonates can be used as accelerators to enhance the early age properties of cementitious materials. Bicarbonates like KHCO3 and NaHCO3 could form strong alkali (KOH, NaOH) and cause potential risk of alkali-silica reaction. Ca(HCO3)2 could serve as a better accelerator than these bicarbonates because of formation of CaCO3 and Ca(OH)2, which are usually found in cementitious system. The effects of Ca(HCO3)2 on the hydration and physical properties of OPC paste were studied through heat of hydration, setting time, extension degree, compressive strength, pore size distribution, TG-DTA, XRD and SEM tests. The results showed that Ca(HCO3)2 can accelerate the formation of ettringite and CO2-AFm at the initial stage, and increase the early age strength of OPC paste. Besides, Ca(HCO3)2 was found to accelerate the hydration of C3S and C2S at a later stage and modify the pore structure of OPC paste. The reaction between Ca(HCO3)2 and portlandite formed CaCO3, which could fill the harmful pores in cement paste. The optimum content of Ca(HCO3)2 was found to be 1% by weight of cement, and further increase of Ca(HCO3)2 could decrease the compressive strength by increasing the harmful pores.

In the present study, thermal and mechanical characteristics of cement mortar incorporating Ceramic Waste Powder (CWP) as cement replacement were examined. The cement of the mortar mixes has been replaced with CWP which was provided from Almas-Kavir Company (Iran) in amounts of 5%, 10%, 15%, 20% and 25% (by weight of cement). The mortar specimens were cured in water for 28 days, and then the hardened specimens were exposed to temperatures of 200 °C, 400 °C, 600 °C, and 800 °C. This paper represents the thermal performance of CWP as cement replacement based mortar, including the mechanical strengths, mass loss, dry bulk density, ultrasonic pulse velocity and total porosity of the cement mortars. The X-Ray Diffraction (XRD) and Scanning Electron Micrograph (SEM) analyses of mentioned mortars have been also measured to explore the microstructure of heat treated specimens. Additionally, surface cracks of the mortar specimens were examined. Experimental results explain that specimens containing CWP exhibit higher compressive and flexural strengths than control specimens at elevated temperature. The study has also shown that mortar specimens containing CWP improved the thermal resistance of mixes. The XRD analyses showed that the mixes containing CWP have a lower intensity of portlandite peaks than the control mix, and SEM images explained that using CWP reduced the porosity. It should be mentioned that incorporating CWP as cement replacement improved several characteristics at elevated temperatures.

An experimental study of ordinary Portland cement mixed with ground granulated blast-furnace slag (OPC-slag) showed varying rates of slag (60%, 40%, and 20% replacement rate to OPC) and polyaluminum chloride (PAC) (0%, 2%, 4%, 6%, 8%, and 10% added to the mixing water) were mixed into the cement to assess the strength and pore structure properties of the cement. X-ray diffractometer, mercury introsion porosimetry, scanning electron microscopy and thermal analysis were performed to observe the pore structures and hydration reactants. As the amount of PAC increased, the compressive strength increased, the total porosity decreased, and the pore volume less than 50 nm diameter increased. PAC promotes hydration of slag particles. The aluminum contained in the PAC also changes the C-S-H gel to a more dense C-A-S-H gel and contributes to the formation of Friedel’s salt. And the chloride ion in the PAC forms a Friedel’s salt to fill the pores. In this process, portlandite was consumed. 10% PAC showed the highest compressive strength at all slag replacement rates. 20% slag showed 134.6% at 28 days, 151.9% at 7 days for 40% slag, and 159.0% at 1 day for 60% slag. 10% PAC decreased total porosity and increased pores smaller than 50 nm compared to without-PAC sample. In particular, the OPC-slag sample with 20% slag substitution showed the largest pore structure change due to the large and clear reduction effect of pore diameter and volume by PAC. It was confirmed that mixing of PAC with OPC-slag cement paste formed a dense matrix and affected the improvement of compressive strength and the change of pore structure.

Powerful synergies between phosphonate, zinc oxide, and acrylamido-tert-butyl-sulfonate (ATBS) copolymer chemical additives render superior performance in a high-temperature retarder system for oil well grade Portland cement. The phosphonate retarder and ATBS-based retarders establish a two-tiered strength development where amorphous C-S-H converts to crystalline dicalcium silicate hydrate (C2SH) in the first (low compressive strength) tier prior to the reaction of Portlandite with quartz. The three additive retarder system can be tuned with nanosilica to eliminate the two-tiered strength development effect leading to a smooth transition from the cement in the slurry form directly to its highest compressive strength.