Age Hydration Research Articles

Effect of fly ash and nano Silica on the formation and evolution of Calcium Silicate Hydrate in Portland Cement during hydration process

Recently, the trend of replacing cement with mineral admixtures in concrete has witnessed increasing interest in the construction industry due to the reduction in embodied energy and CO2 emissions. However, the addition of these admixtures in Portland Cement (PC) affected the formation as well as the structure of the hydration product Calcium-Silicate-Hydrate (C-S-H), which is reflected in the mechanical and durability properties of cement concrete. In the present study, nano-silica (NS) and a mixture of fly ash (FA) and NS were replaced into PC (PC + 0.5 % NS, PC + 1 % NS, PC + 0.5 % NS + 20 % FA and PC + 1 % NS + 40 % FA) to systematically study the formation and structural evolution of hydration products, namely C-S-H, at atomic and micro-scales at the early stage of hydration (3 days) and a later stage of hydration (90 days). The formation and structure of C-S-H were analyzed to correlate the microstructure development by using XRD, Rietveld technique, FESEM, TEM, FTIR and nano-scale mechanical properties by employing the nanoindentation techniques. Atomic Pair Distribution Function (PDF) is used to understand the effect of admixtures on the C-S-H structure from atomic point of view. PDF shows the structural modification of C-S-H such as different polyhedral, separation of intralayer/interlayer, pair/bond length, coordination number of atoms corresponding to the addition of additives with hydration age. Also, porosity measurements show increasing or decreasing porosity during hydration with additives. It is observed that the contribution of low-density C-S-H (LD C-S-H) is greater than that of high-density C-S-H (HD C-S-H) in the beginning days, whereas HD C-S-H more than LD C-S-H in the latter days of hydration. The elastic modulus increased from 15.44 GPa to 19.82 GPa and the hardness decreased from 0.41 GPa to 0.35 GPa of LD C-S-H in early days, whereas elastic modulus decreased from 34.84 GPa to 29.33 GPa and the hardness increased from 0.75 GPa to 0.83 GPa of HD C-S-H in the latter stage due to addition of additives. However, both increased for LD C-S-H and HD C-S-H for each corresponding mixture during hydration. The present study reported the formation and microstructural modifications of C-S-H and the correlation with nano-mechanical properties due to addition of nano or micro-sized admixtures (nano silica and fly ash) in the cement system. This correlation helps to develop low-energy cement composites by tailoring cement systems with desired properties.

The influence of low temperature rise polymer on early cement hydration from the point of view of hydration kinetics and thermodynamics

The key to studying the influence mechanism of additives on the cement hydration process lies in revealing the influence process of admixtures on the evolution of chemical driving forces of relevant phases in the cement hydration process. This study is the first to adopt the Krstulovic-Dabic (K-D) kinetic model to investigate the hydration mechanism and kinetic parameters of a cement system with a low-temperature polymer (CAMC). Gibbs Energy Minimization Selektor (GEMS) was used for pore solution composition analysis of cementitious system and calculation of saturation index. The results show that the exponent and reaction rate constant of the (K-D) model decrease with the increase of hydration age and CAMC content, with K1 significantly greater than K2 and K3 being the smallest. The saturation index of calcium hydroxide (CH) and ettringite (AFt) is greater than 0, indicating that both phases are supersaturated in all samples. The transition time from supersaturation to undersaturation of gypsum is delayed, confirming the delayed consumption of gypsum by CAMC. This provides new insights into the effects of admixtures on cement hydration and the mechanisms of cement hydration.

A chloride diffusion model for cementitious material with pore-solution viscosity enhancement

A promising approach to retard chloride attack has been proposed by increasing the pore solution viscosity in contrast to the traditional methods, but the dependence of chloride diffusion coefficient on viscosity has not been included in the current transport models. This paper presents a model for the diffusion of chloride in cementitious materials based on the viscosity-enhancing behavior of pore solution using viscosity modifying admixtures (VMAs). The parameters affecting the diffusion of chloride in the viscosity-enhancing solution are proposed to be the VMA molecular shape factor and VMA volume fraction based on the Maxwell approximation of spherical inclusions in the effective medium approximation theory. VMA shape factor is modeled with VMA molecular mass as a key variable. VMA volume fraction is calculated as a function of water-cement ratio, hydration age, initial VMA volume fraction, and VMA leaching residual fraction. This chloride diffusion model is developed and validated, which is based on the modification of Fick's second law and takes into account the pore solution viscosity-enhancing behavior and VMA-induced pore coarsening. This model differs from traditional models based on ion transport paths and provides a new reference for concrete durability design in terms of the intrinsic properties of the pore solution.

Evaluation of hydration behavior of cement-stabilized macadam via electrochemical impedance spectroscopy

Electrochemical Impedance Spectroscopy (EIS) was an important method for continuous and non-destructive monitoring of cement hydration process. The EIS, porosity and compressive strength of cement-stabilized macadam with different structures and cement content at different hydration ages were tested. By fitting the quasi-Randles equivalent circuit model, the electrochemical parameters were obtained to analyze the hydration degree and microstructure changes of materials during the hydration process. The mathematical models of electrochemical parameters and hydration parameters in skeleton dense structure, suspension dense structure and skeleton pore structure were established. The results show that the electrochemical parameters of the quist-Randles equivalent circuits model had a fine correlation with the hydration parameters of cement-stabilized macadam materials. The impedance curves of different cement-stabilized macadam structures had the same variation laws under different cement contents. As the hydration age increased, more hydration products formed and filled the internal pores of the structure, leading to the gradual formation of a dense structure in the material, further reducing the porosity and increasing the pore solution resistance RS. Meanwhile, the increase in cement content also led to a gradual increase in the compressive strength of the sample. The research results show that Rs was inversely proportional to porosity and had a good logarithmic relationship with compressive strength.

The synergistic mechanism of hydration regulation and carbonation curing on the carbon sequestration and impermeability enhancement of cementitious materials

Carbonation curing, as a novel curing method, gradually plays an important role in the reduction of carbon emissions and the improvement of durability for cementitious materials. This study considers the intervention of carbonation at different ages of hydration and investigates the synergistic effect of nano-titanium dioxide (NT) regulating cement hydration and 20% CO2 carbonation curing on the enhancement of carbon sequestration and durability performance of cement mortar. The results show that early-age carbonation curing and the addition of NT increase the unit area carbon sequestration of cement mortar at the age of 28 days by 242.75% (0.41 kg/m2); meanwhile, some micro-nano-sized calcite crystals and NT jointly play a nucleation and filling role during hydration, optimizing the pore structure. As a result, the unit area capillary water absorption coefficient and gas permeability coefficient decrease by 70.55% and 91.89%, respectively, inhibiting the continuous diffusion of CO2 and achieving controlled surface carbonation. Based on the pore characteristics of the carbonated surface, this study also proposes a “Sieve filter” structure hypothesis model, which suggests a negative correlation between pore structure and surface depth under the synergistic mechanism. This can provide innovative ideas for the cement industry to enhance the durability performance of reinforced concrete prefabricated components using carbon sequestration technology.

Effect of nano-metakaolin on the chloride diffusion resistance of cement mortar with addition of fly ash

This study examines the improvement of nano-metakaolin (NMK) on the chloride ion diffusion resistance (CDR) of fly ash (FA) cement-based materials. The rapid chloride diffusion (RCM) method was employed to compare the effects of nano Al2O3, nano CaCO3, nano SiO2, nano attapulgite clay, and NMK on the CDR of cement mortar, and a suitable nanomaterial was identified. Subsequently, the influence of NMK on the CDR, flexural and compressive strengths of FA cement mortar was examined. The chloride ion concentration of NMK/FA cement paste under simulated salt environment were measured. The action mechanism of NMK on the CDR of FA cement mortar was explored through mercury intrusion porosimetry and scanning electron microscopy tests. The results reveal that among these nanomaterials, NMK exhibited the highest cost-effectiveness in enhancing CDR of cement mortar, with a suitable content of 5 wt%. NMK demonstrated a significant improvement in the CDR of FA cement mortar, particularly at a hydration age of 7d. Incorporating 5 wt% NMK into the cement mortar with addition of 30 wt% FA resulted in a 73% reduction in chloride ion diffusion coefficient (Dcl) compared to the cement mortar with the addition of 30 wt% FA at 7d. NMK enhances both flexural and compressive strengths of FA cement mortar at various hydration ages (3, 7, 14, 28 d). The addition of 5 wt% NMK makes a increment of about 10% for the flexural strength of cement mortar with 30 wt% FA at 7d. Moreover, NMK results in a denser internal structure of FA cement mortar, facilitates the generation of C–S–H gel, and reduces the more-harmful pores and harmful pores while increasing harmless and of less-harmful pores cement paste. Additionally, NMK exhibited the most substantial reduction in chloride ion concentration within FA cement paste at 7d. In general, NMK significantly enhances CDR, flexural and compressive strengths of FA cement mortar, especially at a hydration age of 7d.

Study on the Properties of Belite Calcium Sulfoaluminate Cement–Ordinary Portland Cement Composite Cementitious System

Due to low early strength and high shrinkage, ordinary Portland cement (OPC) has difficulty meeting the actual needs of modern construction projects, while belite calcium sulfoaluminate cement (BCSA–OPC) composite cement provides a new solution. The mechanical and the drying shrinkage properties of the BCSA–OPC mortar were determined, the hydration heat of the BCSA–OPC was studied, and the pore size distribution of the mortar was investigated. In addition, the hydration products of the BCSA–OPC were analyzed by X-ray diffraction (XRD) and simultaneous thermal analysis (TG-DSC), and the microscopic morphology of the BCSA–OPC mortar was observed by scanning electron microscopy (SEM). The results show that with the increase in BCSA dosage in the BCSA–OPC, compared with OPC, the flexural strengths of the mortar of 50% dosage of BCSA at the hydration age of 1 d, 3 d, 7 d, and 28 d are improved by 33.3%, 36.6%, 23.6%, and 26.8%, and the compressive strengths are improved by 50.8%, 35.7%, 13.4%, and 27.7%. The drying shrinkage and total porosity of the mortar at the hydration age of 28 d are reduced by 117.4% and 21.55%, respectively. It is attributed to the filling effect of a large amount of ettringite (AFt) and intertwined with the fibrous C-S-H gel to form a network. This study will provide a theoretical basis for the application of the BCSA–OPC engineering.

Understanding the influence of ultrasonic power on the hydration of cement paste

This paper studied the dispersion and hydration of cement paste prepared by power ultrasound (PUS)-assisted mixing technology. The ultrasonic power used were 0 W, 480 W and 912 W. The hydration process and microstructure were tested by using isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric-differential scanning calorimetry (TG-DSC), solid-state nuclear magnetic resonance silicon (29Si-NMR) spectroscopy, mercury intrusion porosimetry (MIP), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (SEM‒EDS). The results indicated that the dynamic hydration kinetics of cement paste under ultrasonic irradiation can be categorized into crystallization nucleation and growth (NG), phase boundary (I) and diffusion (D) processes. The apparent rate constant KNG in the NG process and KI in the I process both increased as the ultrasonic power increased, suggesting that PUS-assisted mixing accelerated the early hydration process. PUS shortened the dormant period and enhanced the total hydration heat release. The capillary pores and gel pores were both reduced at 28 days. Similarly, compared with those of C0 and C480, the gel porosities of C912 decreased by 35.17% and 31.87%, respectively. In addition, the mean chain length of the C–S–H gel increased with increasing ultrasonic power, which effectively filled the nanoscale defects. PUS improved the early strength and increased the strength at late hydration ages. Compared with that in the reference group, the compressive strength in the C912 group was enhanced by 26.1% at 1 day and 18.3% at 28 days. These findings demonstrate that power ultrasound-assisted mixing is advantageous for enhancing the sustainability of building materials, thereby contributing to the development of future circular buildings.

Effect of blast furnace slag substitution for cement in carbon-reduced and low-cost solidified/stabilized cementitious materials

The development of low-carbon cementitious materials involves the selection of the appropriate raw materials and the transformation of the hydration mechanism. In this study, low-carbon and low-cost cementitious materials were prepared using municipal solid waste incineration fly ash (MSWI FA), blast furnace slag (BFS), and desulfurization gypsum (DFG) as raw materials to reduce clinker usage. Results showed that the compressive strength of K5 (mass ratio of BFS: DFG: MSWI FA = 7:1:2) after 360 d of curing was 41.49 MPa, with a low leaching concentration of heavy metal residues that meet groundwater Class II standards, a dioxin content of only 25 ngTEG/kg, and a stable pH value ranging between 11 and 11.5. Microscopic analysis revealed a continuous decrease in the Ca/Si atomic ratios of K4 (mass ratio of BFS: DFG: MSWI FA: P·I 42.5 = 42:10:20:28) and K5, i.e., 1.18–1.54 and 1.04–1.23, respectively, with the increase in the hydration age. The highest Al/Si atomic ratio of K5, i.e., 0.26–0.31, was observed with the strongest conversion trend of calcium–silicate–hydrate gel into calcium–aluminum–silicate–hydrate gel, and the network structure of sodium–(calcium)–aluminum–silicate–hydrate gel zeolite-like phase was generated. The water-to-binder (WTB) mass ratio of 0.35 was determined to be more suitable for the K4 and K5 systems and resulted in a 56.83% and 90.82% reduction in half-life t∂ compared with the WTB ratio of 0.5, respectively. Notably, the value of the reaction velocity constant K in the induction period was 10 times that of K1, and the autocatalytic reaction controlled the value of N to < 1. The X-ray absorption near-edge structure indicated that Zn solidification produced Zn2SiO4 with a small solubility product. The production of 1 t of K5 emitted only 10.83 kg/t of CO2, which was 40 times less than that of K1. Overall, K5 provides the highest economic benefit at 40.08 USD/t, and the clinker-free cementitious system with multisolid waste synergy has significant advantages in terms of solidifying harmful substances, reducing carbon emissions, and lowering costs.

Ultrasonic monitoring of hydration behavior of cement paste doped with triethanolamine using novel piezoelectric ultrasonic transducer

The propagation of ultrasonic wave in cement paste is closely related to its physical properties, and therefore shows a potential application in fields of online monitoring of hydration and hardening properties of the cementitious materials. Here, the hydration characteristics of cement paste doped with triethanolamine were studied based on the ultrasonic transmission method using the tailor-made horizontal omnidirectional piezoelectric ultrasonic transducer. The results show that clear ultrasonic waveforms can be observed at hydration age of 2 h. The dominant frequency of the reception wave is low at early hydration age and shifts towards the high frequency direction with hydration. The amplitude of the head wave increases sharply before hydration of 24 h, and the increasing extent decreases gradually until hydration of 166 h. The hydration process of cement at early hydration age can be classified into three stages based on amplitude changes of the head wave, that is, the induction period before 4 h, the acceleration period during 4–12 h, and the deceleration period after 12 h. The acoustic parameters of cement paste at early hydration age conform well to the logistic function distribution. The research finding might provide a new method to estimate hydration and hardening properties of cementitious materials, especially on large construction sites.

Estudo preliminar do efeito da cura por carbonatação em geopolímeros

Abstract Carbonation curing differs from weathering carbonation since it is performed intentionally at the early ages of cement hydration. This cure involves applying different levels of CO2 (5% to 99%) to concrete for a short period of time, usually followed by conventional hydration. The objective of this article was to evaluate the carbonation curing in metakaolin-based geopolymer concretes, activated with NaOH and Na2SiO3, and compare them with Portland cement (PC) concrete. The following tests were applied: determination of pH, carbonation depth, water absorption by immersion, void index, and compressive strength. The results showed that after the carbonation curing, the geopolymer concrete had compressive strength and carbonation depth equivalent to the concrete with PC, but with a lower absorbed CO2 content. Although this type of cement absorbs less CO2 but is more sensitive to carbonation. The effect on the void ratio was not remarkable. Furthermore, the alkalinity of concretes can be partially recovered after subsequent curing by water immersion.

The Combined Effect of Nanoclay Powder and Curing Time on the Properties of Class G Cement

When the cement paste is subjected to stresses, the cement matrix and its characteristics are dramatically influenced, especially in the early ages of cement hydration when the cement properties have not yet settled. Nanoclay, which is made up of very small particles, was used to improve the properties of cement. In this study, the early-age performance of cement made with nanoclay powder for use in oil wells is assessed. Ten cement samples were made and cured at varying times (6, 12, 24, 48, and 72 hours), wherein 1% by weight of cement of nanoclay was used in five samples, and in the other five samples, there was no nanoclay present in the cement. Failure properties, petrophysical parameters, and elastic properties were studied for all the cement samples. Nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were all used to describe the cement samples and determine how different curing times affected the cement’s mineralogical and microstructural features. The results displayed that compressive and tensile strengths were shown to increase with curing time for both the base (control) and nanoclay cement samples; however, the compressive and tensile strengths of the nanoclay cement samples were found to be greater than the base sample by 20.2% and 17.9%, respectively. This is due to the presence of more calcium silicate hydrate in these samples. Nanoclay cement had 76.9% lower permeability than control cement, which can be related to the capacity of the nanoclay particles to fill the microstructure dominating the base samples as curing time increased. Young’s modulus of the cement was lowered by 1.8%, while Poisson’s ratio was increased by 2.7% when nanoclay was incorporated. Nanoclay cement has a 29.2% smaller porosity than regular cement, and this porosity increases as the cement cures. The novelty of this work is that several properties of the class G cement were evaluated at the early stage of hydration, where the nanoclay particles were used to improve these properties.

Influence of negative temperature hardening on hydration, pore structure evolution and strength development of cement paste

The pre-cured 24-h demolded cement pastes were directly cured at −5 °C and +20 °C for different ages to investigate the influence of negative temperature hardening on hydration, pore structure evolution, and strength development. Thermogravimetric (TG) results show that the inhibition effect of negative temperature hardening on the hydration degree and C–S–H gel content is different. As the hydration age increases to 120 days, the hydration degree and gel-space ratio of negative temperature hardening cement paste can reach the positive temperature hardening level of 120 days, while the C–S–H gel content is still lower than the positive temperature hardening level of 120 days. Mercury intrusion porosimetry (MIP) results indicated that negative temperature hardening increases all types of pore volumes, especially the pore volume of <10 nm. Similar to the hydration degree, by giving sufficient negative temperature hardening time (120 days), the pore characteristic parameters of negative temperature hardening cement pastes can approach the level of 120-day positive temperature hardening. Also, the fractal analysis shows that negative temperature hardening increases the proportion of large-diameter pores in the range of <100 nm, and decreases the proportion of large-diameter pores in the range of >3000 nm. In addition, the micro-mechanisms of limiting strength development are different at different negative temperature hardening stages. The early strength development is affected by the coupled effects of hydration and pore structure, while the later strength development is limited due to the lower C–S–H gel content.

Acoustic behaviour of Portland cement paste with sodium gluconate additive during hydration

The ultrasonic pitch–catch method was used to study the hydration behaviour of Portland cement paste with sodium gluconate (SG) additive using a tailor-made piezoelectric transducer. X-ray diffraction analysis showed that the intensity of the diffraction peak of calcium hydroxide decreased with increasing SG content (CSG), especially for CSG &gt; 0.10 wt%. The compressive strength of the hardening cement pastes decreased remarkably for the pastes with CSG &gt; 0.05 wt%. Ultrasonic waveforms appeared after 2 h of hydration and the waveform amplitudes of cement pastes with SG contents of 0.15 wt% and 0.20 wt% were obviously larger than those of cement pastes with CSG = 0.05 wt% in the early hydration stage. The hydration process of the cement paste over 300 h was classified into three stages based on the head wave amplitude variation – the fluctuation period, the rapidly increasing period and the smoothly increasing period. The acoustic propagation time changed greatly with hydration before a hydration age of 48 h, indicating that the hydration and hardening process of the cement paste was intense in the first 48 h. The proposed ultrasonic monitoring method opens a new perspective for studying the hydration behaviour of SG-blended cement paste.

Manufacture of eco-friendly cementitious building materials of high performance from Egyptian industrial solid wastes

One of the goals of modern societal development is to achieve environmental sustainability by expanding the number of smart cities with eco-friendly buildings. A research was carried out to investigate the possibility of utilizing Egyptian industrial solid wastes from factories to create sustainable construction materials in order to accomplish this goal. Along with various waste products including cement kiln dust (CKD) and silica fume (SF), which were chemically categorized, the investigation identified metakaolin (MK) and dealuminated kaolin (DK). Various dry mixes were used to determine the hydration characteristics of the binders, including MK-CKD, DK-CKD, OPC-DK, DK-CKD-SF, MK-CKD-SF, and OPC-DK-SF.The physico-chemical and mechanical properties of the cement pastes were analyzed using compressive strength (CS), chemically combined water (Wn, %), and free lime (CaO, %) content over time. The hydration products were identified using differential scanning calorimetry (DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Scanning electron microscopy (SEM) analyses. The findings revealed that DK had a larger surface area (95 m2/g) than MK and displayed greater pozzolanic activity, particularly during early hydration. Moreover, the inclusion of SF provided further densification of the microstructure of the hardened DK-CKD-SF and/or OPC–DK–SF pastes.According to the findings, the OPC-DK pozzolanic cement pastes had a denser structure than the neat OPC paste. Moreover, the inclusion of SF resulted in additional densification of the microstructure of the hardened OPC-DK-SF pastes, which was evident in the observed increase in compressive strength values at all ages of hydration. The use of industrial solid waste as a sustainable building material has the potential to assist Egypt in meeting its goals for sustainable development and climate protection.

Non-destructive tests to evaluate the self-healing capacity for a 3D printing ECC material

The conventional construction sector is the one that generates CO2 emissions, as well as waste generation. Faced with this problem, 3D printing has positioned itself as an alternative. Therefore, in recent years, interest in cement-based material for 3D printing has increased in the construction sector as a partial or total replacement for conventional construction methods. However, 3D printing, despite being a novel technique, has some drawbacks, one of the biggest threats being the generation of cracks or microcraks that appears by the transport or the design of the 3D printed figures. These cracks can cause major structural and durability problems in the final application. Numerous materials have been developed to meet the requirements of 3D printing. Nevertheless, there are few publications on materials that are able to be printed in 3D and have an autogenous self-healing capacity. Therefore, in this study, we are working on the development of an Engineered Cementitious Composites (ECC) material, also known as Strain Hardening Cementitious Composites (SHCC) that has the characteristics to achieve structural integrity, durability, reliability, and robustness of 3D printing (ECC-A3D).This paper describes the experimental procedure of an ECC material in two different environments (at room temperature, 34 ± 2% RH and 20 ± 2 °C, and curing chamber 98 ± 2% RH and 20 ± 2 °C). The characterization of the ECC-A3D material is studied by fresh properties, consistency, open time, extrudability and buildability and hardened properties, compressive and flexural strength up to 90 days. A 3D printing material has been achieved that reaches a value of 16.54 MPa and 50.82 MPa in flexural and compression at the hydration age of 28 days at room temperature, and 17.13 MPa and 58.26 MPa in curing chamber. The self-healing behavior of ECC is evaluated by three non-destructive methods: absorption and sorptivity tests, optical microscopy, and micro-computed tomography, confirming a reduction in absorption and crack healing during hydration time.

Quantitative study on growth and porosity of C-S-H structures: Experiments and simulations

Coupling of microstructural and physico-chemical modelling of cement hydration is a key step towards prediction of material performance. In this paper, a physico-chemical model based on surface reactions and ion transports is proposed to capture the development of calcium-silicate-hydrate (C-S-H) not only at an early age but also at later ages of hydration (e.g, up to 28 days). Furthermore, we introduce a random sampling method to quantify pore size distribution and phase fractions in the 3D simulation, which are available for the comparison with experimental data. The latest experimental techniques were used to quantify the development of the C-S-H as well as its pore sizes, e.g. SEM, 1H NMR , XRD during hydration. By combining observations from experiments and simulations, we can explain the densification of C-S-H during the hydration.

Cementitious phase quantification using deep learning

This study investigates deep learning-based backscattered electron (BSE) image segmentation as a novel approach to automatise phase quantification of cementitious materials and estimate their degree of hydration and porosity. The case study was on Portland cement paste that hydrated from 1 day to 2 years. The initial findings suggest that using arbitrary thresholds for phase segmentation, a strong correlation can be established between the results from BSE image analysis, quantitative XRD, and EDS/BSE, particularly for samples with a hydration age >28 days. The second part demonstrates the success of automated image segmentation that relies on learning the material composition from a meticulously analysed image database, which can then predict the content of numerous other images within seconds. This novel approach can turn the analysis of cementitious materials' phase composition from a tedious process that requires specialised equipment and expertise into a routine test for quality control.

Experimental Study on the Strength and Hydration Products of Cement Mortar with Hybrid Recycled Powders Based Industrial-Construction Residue Cement Stabilization of Crushed Aggregate.

The strength-formation mechanism for industrial-construction residue cement stabilization of crushed aggregate (IRCSCA) is not clear. To expand the application range for recycled micro-powders in road engineering, the dosages of eco-friendly hybrid recycled powders (HRPs) with different proportions of RBP and RCP affecting the strengths of cement-fly ash mortar at different ages, and the strength-formation mechanism, were studied with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the early strength of the mortar was 2.62 times higher than that of the reference specimen when a 3/2 mass ratio of brick powder and concrete powder was mixed to form the HRP and replace some of the cement. With increasing HRP content substituted for fly ash, the strength of the cement mortar first increased and then decreased. When the HRP content was 35%, the compressive strength of the mortar was 1.56 times higher than that of the reference specimen, and the flexural strength was 1.51 times higher; XRD and SEM studies of the hydrated cement mixed with HRP showed that the amount of CH in the cement paste was reduced by the pozzolanic reaction of HRP at later hydration ages, and it was very useful in improving the compactness of the mortar. The XRD spectrum of the cement paste made with HRP indicated that the CH crystal plane orientation index R, with a diffraction angle peak of approximately 34.0, was consistent with the cement slurry strength evolution law, and this research provides a reference for the application of HRP to produce IRCSCA.

Water-resistance performance analysis of Portland composite concrete containing waterproofing liquid membrane

Portland composite cement (PCC) is well-known as a low-carbon and low-cost cement as compared to Ordinary Portland cement (OPC). Hence, PCC is broadly used for infrastructure development. The concerning issue is that PCC concrete show low strength than OPC concrete as PCC contains 30%–35% supplementary materials and 65%–70% clinker. Consequently, PCC concrete exhibits little waterproofing performance, which limits the application of PCC composites in the heavy rainy regions and design of water structures. The current research aims to improve the water-resistant quality of PCC concrete using the waterproofing chemical liquid admixture namely Sika® Membrane-2000. Different dosages of admixture like 1%, 1.5% and 2% of cement were introduced to prepare the PCC concrete compositions and examined the physico-mechanical and microstructural properties at different hydration ages. It was revealed that PCC concrete with water to binder ratio 0.40 and 1.5% admixture shown the attainment of good structural density and formation of low voids, which were closer to plain OPC concrete. In addition, water absorption was reported around 3% and 6% at 28d at static and non-static water condition, respectively for solid cube and concrete wall composed with PCC-1.5%. Moreover, CS and STS were observed about 34 MPa and 4 MPa at 28d, correspondingly which is very near to OPC specimens. Investigations of microstructures by SEM and EDS for PCC-1.5% sample also detected the compactness of hydration products and development of recognized crystals like calcium silicate hydrate, ettringite and calcium sulfoaluminate, which is corroborated with the physical and mechanical strength properties of PCC-1.5% concrete. The results of this research might be applied in the constructures works of water-resisting issue with low-cost.