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Understanding the stress–strain behaviour of cement-based materials is important for the performance modelling of concrete structures. This work studied the stress–strain behaviour of cement paste under a triaxial stress state with varying confining pressures. The influence of confining pressure on peak stress, peak strain and volume change was studied using the experimental results obtained from cement paste samples with compressive strengths of 28 and 35 MPa. The samples were tested under four confining pressures (0, 5, 10 and 15 MPa). A simple equation for the strain at peak compressive strength was developed from linear regression analysis of the test data and available results in the literature. The commonly used stress–strain model for concrete was adopted to model the behaviour of cement paste. A functional relationship for model parameters was developed and calibrated using the experimental results. As expected, the obtained results demonstrated that the strength and ductility of cement pastes are significantly improved due to confinement. The relationship between lateral and axial strains was found to be linear. Overall, the proposed model showed good agreement with the experimental results and can be used to numerically analyse structures with cement paste (e.g. oil wells).

The effects of limestone powder (LP) of different fineness on the packing density, strength and hydration behaviour of cement blended with a high volume of LP were studied using Vicat setting time tests, strength tests, isothermal calorimetry and scanning electron microscopy. Three different LP fineness values were examined and it was found that cement replacement by LP with the smallest median particle size produced the highest density. The compressive strength of the blended cement mortar increased with increasing LP fineness. The packing densities of the blended cement were used to infer the evolution of mechanical strength of the blended cement mortar. The addition of LP with a median particle size smaller than that of cement accelerated the hydration of cement in the acceleration period. Compared with LP with a median particle size smaller than that of cement, the production rate of nuclei of cement blended LP with a median particle size larger than that of cement decreased with increasing amounts of LP replacement, while the growth rate of nuclei increased with increasing amounts of LP replacement.

The durability of ultra-high-performance concrete (UHPC) exposed to freezing–thawing (F–T) is closely associated with its micromechanical properties. In this study, the nanoindentation technique is employed to characterise the micromechanical properties of UHPC at different F–T cycles. It is observed that the indentation moduli of low-density calcium silicate hydrate, high-density calcium silicate hydrate, and calcium hydroxide in the studied UHPC decrease moderately with the decreasing ranges of 11.58, 14.56 and 3.3%, respectively, after undergoing 1500 F–T cycles. More micropores gradually form, converge and connect, and the volume fraction of micropores increases up to about 120%. The interfacial transition zone (ITZ) between steel fibre and cement paste is more prone to act as the weakest zone than that between fine sand and cement paste. The thickness of ITZ enlarges from 22 μm of the unconditioned stage to 60 μm at 1500 F–T cycles. Based on the micromechanical properties obtained from the nanoindentation test, the modulus of elasticity values of UHPC under different F–T cycles are predicted using the multiscale homogenisation model. It is proved that the combined micromechanical characterisation and multiscale homogenisation technique is capable of predicting the macromechanical properties of UHPC and their changes under F–T action.

This study explores the influence of partial replacement of high reactivity Attapulgite (HRA) with cement by weight and evaluate the effect of curing temperatures on the compressive strength of modified cement paste (MCP). Recently, the Iraqi clay(Attapulgite) has been processed to pozzolanic material HRA, after extracting it from the quarry the clays crushed and grind to filler then specific the suitable calcinations temperature to make this clays as a pozolznic material. The possibility of replacing the Iraqi clays with cement can be reduce the cost and the impact of cement manufacturing on environment. In this study, three percentages of high reactivity Attapulgite used as a replacement 0, 10 and 20 % by weight of cement. The samples cured in four temperatures 20, 40, 60 and 80 °C. The samples with dimension 50x50x50 mm3 were casted and tested at ages 7, and 28 days. The test result shows that the compressive strength at early ages without HRA and cured at 20 °C were higher than samples with HRA. The maximum percentage of HRA as a replacement with cement has a reduced the compressive strength of the concrete. The result at 28 days for the samples with 10% of HRA at curing temperature 40 °C shows increased in compressive strength up to 60 °C, while when the samples were cured at curing temperature 80 °C shows decreased the compressive strength.

In order to investigate the difference between internal and external hydration of hardened cement paste under microwave curing, a comparative study on the hydration products, hydration degree, fracture morphology, and pore structure between the inner part and outer part of hardened cement paste (Φ120 mm × 120 mm) under microwave curing was carried out by XRD-Rietveld refinement, TG-DSC, SEM, and MIP methods. The results show that the total hydration degree of the inner part is lower at early ages, but with the hydration, there is little difference in the hydration degree between inner and outer parts at later ages. Apart from granular AFt crystal formed in the inner part of hardened cement paste, there is little difference in the fracture morphology between internal and external hydration. The total porosity of the outer part is lower than that of the inner part.

The effect of graphene oxide (GO) nanosheets on the spatial distribution of cement paste pores has been investigated. In this study, a scheme based on the radial distribution function is developed to analyze the spatial distribution of pores in GO-cement composites. By applying the developed scheme, the addition of 0.04% GO is found to reduce the spatial inhomogeneity of pores in cement paste by around 20% at all curing ages. The test results show that the compressive strength of the cement paste sample containing GO is increased by 30-40%, indicating the negative correlation between the spatial inhomogeneity of pores and mechanical properties of GO-cement composites. Besides the spatial homogenization effect of GO on pores, pore structure refinement by GO is also found to increase the mechanical properties of cementitious materials. The findings suggest the great potential of using GO to modify cementitious materials by homogenizing the spatial distribution of pores. The spatial distribution analysis scheme presented in this study can be used for the future structure-property study of nanoengineered cementitious materials with enhanced performance.

Recent experimental investigations on the nanoscale of hardened cement paste revealed that the tensile strengths of the microstructural phases present amount to several hundreds of MPa. Confrontation with macroscopic tensile strength testing, by e.g. Brazilian splitting, shows a decrease over two orders of magnitude. A computational model based on a hierarchical representation of hardened cement paste microstructure is presented in this paper, attempting to shed light on the factors affecting the scaling of strength from the nanoscopic scale up to the macroscopic scale. The model is validated on a case study featuring a Portland-limestone cement paste subjected to an external sulfate attack. Such conditions compromise the nanoscopic integrity of the C-S-H gel as a consequence of the progressive decalcification and affect the overall load-bearing capacity of the macroscopic cement paste specimen.

The effects of curing temperature (23, 40 and 50°C) on the mechanical properties of cement paste and concrete containing glass powder (GP; 0, 10, 20 and 30%) as a cement replacement are investigated. In addition, a new mixing method (NMM) is studied, which involves soaking the GP before adding it to the concrete. The results show that an increase in the immersion time decreases the Na+/Ca2+ ratio for mixes with 10% GP. The amount of dicalcium silicate, tricalcium silicate and portlandite decreases with the increase in curing temperature, indicating the activation of the pozzolanic reaction. The results show a significant increase in the density and compressive strength early in the curing process due to the higher pozzolanic reaction of GP at elevated temperatures. At higher temperatures, the differences between the control and the GP mixes become smaller. The NMM enhances the mechanical behaviour of concrete compared with conventional mixing. An increase in the compressive strength of 30% is obtained at 10% GP.

Cationic asphalt emulsion (CAE) is a type of organic latex that could be used to modify cement hydration products in order to improve the performance of cement paste. In this study, different methodologies were used to investigate the influence of CAE on the process of cement hydration. The results showed that with an increase in the mass ratio of asphalt to cement, the setting time of the cement paste was prolonged while the compressive strength and water absorption of the cement mortar showed obvious reductions. Other techniques were also used to investigate the cement hydration process and the microstructure evolution caused by the addition of CAE, including conductivity measurements, 29Si nuclear magnetic resonance, low-field nuclear magnetic resonance, measurements of chemically bound water and field emission scanning electron microscopy. It was found that the formation of cement hydration products was delayed with an increase in CAE and the microstructure was affected by the CAE in that the pores were separated by asphalt film and the total porosity decreased.

Rubberized concrete is highly effective in areas where more flexibility is required. Compared to standard concrete, rubberized concrete has greater flexibility, impact resistance, and lower unit weight. In this study, sulfuric acid is used in the surface treatment process of rubber particles to strengthen the bonding property of rubber particles and cement paste. Six waste tire rubber crumb contents (0, 10, 15, 20, 25, and 30%) and particle sizes of 0.6–2.36 mm were used as partial replacement of fine aggregate in concrete. Microstructural analyses (EDX, TGA, XRD) are conducted on rubber crumbs to examine rubber’s compatibility before using it in concrete. The fresh, hardened, microstructural properties (SEM and XRD) and stress vs. strain behavior of rubberized concrete are investigated. From the SEM image, it is analyzed that surface treatment improves the bonding properties of rubber particles and cement paste compared to untreated rubber particles. The mechanical properties of rubberized concrete reduce by increasing the rubber crumb in the mix. Still, the results are not much troubling up to 15% replacement level of rubber crumb, and the rubberized concrete has a highly deformable capacity than standard concrete.

During recent decades, alkali-free accelerators have appeared on the market as setting accelerator additives for shotcrete. In this work, copolymers poly(AANa-co-DMAA) with a variation of their charge densities (monomeric molar ratios) were synthesised by aqueous solution polymerisation and characterised by Fourier transform infrared spectroscopy. Then the copolymers were used to optimise the setting behaviour of cement paste in the presence of alkali-free accelerator. The setting times of cement pastes with a combination of alkali-free accelerators and copolymers were tested. Isothermal calorimetry, X-ray diffraction, thermal gravimetric analysis and total organic carbon were also performed to obtain the comprehensive optimisation effects of poly(AANa-co-DMAA). The results clearly show that the capacity of the alkali-free accelerator for shortening the setting time of cement paste was enhanced significantly by introducing poly(AANa-co-DMAA). More AA units in the copolymers have better adsorption capacity, leading to a faster dissolution rate of tricalcium aluminate and the formation of massive ettringite crystals, thus finally the setting time of the cement paste with a combination of alkali-free accelerators and copolymers was shortened markedly compared with that containing alkali-free accelerators alone. The good synergy effect of the copolymers and alkali-free accelerator indicates great potential for practical applications.

The outstanding properties of carbon nanotubes (CNTs) mean they can be considered as potential components of high-performance cementitious composites. However, the major challenges of using CNTs in cement are their agglomeration, poor dispersion and weak interaction with the cement matrix, which can nullify the potential benefits of CNT addition. A method for increasing the interaction between the CNT surface and cement matrix using magnetite (Fe3O4) nanoparticles, which increases the roughness and dispersibility of CNTs, was investigated. Nanocomposites of multi-walled CNTs (MWCNTs) and magnetite were prepared by electrostatic attraction and added to the cement matrix to produce a novel cementitious composite. Fourier transform infrared spectroscopy and transmission electron microscopy analyses revealed the successful preparation of the MWCNT–magnetite hybrid structure. The mechanical, electrical and microstructural features of nanocomposite-reinforced cements were tested. The results revealed that increasing the weight fraction of the nanocomposite reinforcement improved the mechanical properties of the cement paste. Compared with the control, the compressive, flexural and tensile strengths of cement loaded with 0.3 wt% MWCNTs and 0.3 wt% magnetite at 28 days increased by 83%, 104% and 98%, respectively; the porosity and electrical resistivity were reduced by 31% and 48%, respectively. Microstructural studies of the fracture surfaces were also conducted to elucidate the mechanical behaviour of the samples.

This paper presents the simulation of the permeation of saturated cement paste based on a novel pore network model. First, a 2D hydration model of cement particles was developed by extending the work of Zheng et al. 2005 to provide the background for the network construction. Secondly, the establishment of the pore network model and simulation of permeation of saturated cement paste were carried out. The irregular pores between any two hydrated cement particles were linearized with clear distances as the diameters of pores. The straight tubular pores were interconnected with one another to form the network model. During this process, the weighted Voronoi diagram was employed to operate on the graphical expression of the hydrated cement particles. Water permeation in saturated cement paste was simulated to verify the pore network model. Finally, the factors including water–cement ratio, reaction temperature, reaction time and cement particle size that would influence water permeation were numerically investigated.

Hydration of cement systems modified by nano additives requires the understanding of its mechanisms. The present research is focused on the investigation of hydration processes in cement pastes modified by multi-walled carbon nanotubes (MWCNTs) suspension. The ultrasonication method was used for homogenization of MWCNTs in the volume of an aqueous suspension. The hydration of cement pastes was assessed by the calorimetry test. The prolongation of cement hydration in case of modification by MWCNT suspension was observed. The microstructure observation by scanning electron microscopy (SEM) was performed for identification of MWCNT's dispergation in hardened cement pastes and for the observation of cement hydration products. The compressive and flexural strength were tested to evaluate the effect of MWCNT on mechanical properties of hardened cement paste.

For the past few decades innovation in construction material has grown a lot. This leads to special concrete such as self-compacting concrete, geopolymer concrete, self-healing concrete, etc. To prepare a special concrete apart from regular concreting material some sort of special materials was also needed, like mineral and chemical admixtures. Hence it is necessary to study the effect of these admixtures in cement paste and mortar before studying the same in concrete. Hence an attempt is made to study the effect of mineral and chemical admixtures in the fresh and hardened properties of cement paste and mortar. For this study ultrafine natural steatite powder is taken as mineral admixture and polycarboxylic based superplasticizer and glenium stream 2 were taken as chemical admixtures. Ultrafine natural steatite powder was used as additive to cement in various percentages like 0%, 5%, 10%, 15%, 20% and 25%. Superplasticizer and viscosity modifying admixture were taken as 1.5% and 0.5%, respectively. Then various combinations were worked out. To study the fresh property of cement paste consistency, initial setting time and miniature slump cone test were done based on the results yield stress of cement paste also calculated empirically. To study the hardened property compression test on cement mortar was done. Based on the test results it is clear that the addition of ultrafine natural steatite powder increases the water demand hence reduces the workability. On the other hand, it increases the compressive strength up to a certain limit. Adding superplasticizer increases the workability and reduces the water demand and viscosity modifying admixture reduces the bleeding and segregation effects hence increases the compressive strength.

The effect of the water-to-cement ratio on cement paste microstructural development was investigated using electrical resistivity measurements and computer modelling. Three cement pastes with 0.3, 0.35, and 0.4 w/c ratios were used in this study. The electrical resistivity measurements curve as a function of time for the three pastes shows that the lower the w/c ratio the higher the electrical resistivity through the whole time. The effect of overall porosity and initial distances between particles significantly influence the measurements. Although low w/c ratio paste has low liquid electrical resistivity comparing to other samples, still has high bulk electrical at all ages. The influence of particles proximity due to lower water amount was interpreted through monitoring the electrical resistivity development and computer illustration. The demonstration provides more explanation about the importance of water-to-cement ratio. Through the conducted experiments, empirical correlations were developed regard predicting compressive strength and autogenous shrinkage of cement pastes when all parameters are related to porosity. Setting time was also predicted by monitoring the critical points on the electrical resistivity curve. Scanning electron microscopy (SEM) was employed to elucidate the effect of the w/c ratio on the morphology of hydration products, and it was observed that high w/c ratio paste has more fibers per unite area comparing to lower w/c ratio pastes due to the long distances between hydrates for expanding.

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.

Shrinkage of hardened cement paste is a direct result of its desorption isotherm. The relationship between the desorption isotherm and the relative humidity in a hydrating cement paste is mainly controlled by the pore size distribution (nanopores to micropores). There are several hydration models to describe the microstructure of cement paste, but the desorption isotherm and self-desiccation are not direct outputs from those models as they are usually given as constitutive inputs. In this study an attempt was made to fill this gap by predicting the sorption isotherm, the drying shrinkage and the self-desiccation of cement paste directly from the evolution of its microstructure. A simple hydration model was developed to predict the microstructure of Portland cement pastes, as well as the nanostructure of calcium silicate hydrate (C-S-H), considering its densification during cement hydration. Predictions from the model were compared with some recent experimental findings from studies in the literature where the influence of the water-to-cement ratio was evaluated. The main contribution of this work is the integration of nanoscale and microscale material models towards determining the macroscopic properties of cement paste.

Carbonation induced corrosion is one of the major durability issues for reinforced concrete structures. To address this issue, it is essential to understand the underlying mechanism of carbonation by detecting the ingress of the CO2 and carbonation depth quantitatively. This paper demonstrates the potential of Raman spectroscopy, as a powerful technique, to implement quantification analysis of cement paste carbonation. In present work, the correlation between the content of the CO32− and the Raman peak intensity was initially established by using several standard specimens premixed with certain amount of CO32−. The established correlation was then used to investigate the carbonation of the cement paste in a CO2 diffusion scenario, and the results show a good agreement with that obtained by thermogravimetry measurements. Therefore, the feasibility of the Raman spectroscopy to quantify the carbonation degree of the cement paste can be demonstrated.

This study presents a numerical simulation of the mini-slump flow test performed on the Haegerman table, according to EN 1015-3. The two-dimensional axisymmetrical Volume of fluid (VOF) model is used for the calculation. Various scenarios with the different model set up and boundary conditions were calculated to show how the results are affected. Simulations with different lifting velocities were carried out and compared to the case with instantaneous demolding, which is commonly used in numerical simulations. Also, the effect on results is shown between noslip and specific shear boundary conditions on the mold. The results of simulations indicate that mold lifting should be considered in numerical modeling even if calculation time is highly prolonged. Lifting velocities should not exceed the value of 0.2 m/s in order to maintain laminar flow and stablecalculation.

Pervious concrete or non-fine concrete is a simple form of lightweight concrete made by eliminating the use of fine aggregates. As a result of not using fine aggregate in pervious concrete, then created a cavity filled with air and water can be passed. This cavity resulted in reduced density of the concrete as well as the reduced amount of area that needs to be covered by cement paste, thereby reducing the compressive strength. To increase the compressive strength of pervious concrete, in this study will utilize waste material. The waste material is the cocnut shell ash and coconut shell to strengthen the coarse aggregate bonds, so it is expected to increase the compressive strength along with the increase in permeability. Thus, in this study will replace part of the coarse aggregate with coconut shell with percentage 0%, 2,5%, 5%, 7,5%, 10% and partially replace cement with coconut shell ash with percentage 0%, 2,5%, 5%, 7,5%

To solve the disadvantages of weak bonding between the carbon fiber (CF) and the cement matrix, as well as the poor dispersion performance of multi-walled carbon nanotubes (MCNT) in cement paste, h...

The aim of this research was to investigate the effect of the addition of discrete polypropylene fibres (PPF) and curaua fibres (CF) on the early-age autogenous and drying shrinkage of cement pastes. The fibres used were 12 mm long and the volume fraction varied from 0.3 kg/m3 (0.03%) to 2.7 kg/m3 (0.30%). Autogenous, unrestrained and restrained drying shrinkage tests were performed and it was found that the addition of these fibres influenced the different shrinkage behaviours. A significant reduction in autogenous shrinkage was observed in the specimens with 2.7 kg/m3 of CF, especially in the first few hours of curing. Regarding the unrestrained drying shrinkage, the addition of 2.7 kg/m3 of CF led to only a slight improvement (by about 8.5%) and lower fibre contents had little or no influence. The addition of PPF slight reduced the unrestrained drying shrinkage (by about 8.13%) for all the evaluated fibre contents. Both fibres delayed the development of cracks and reduced crack opening during the restrained drying tests. The addition of 2.7 kg/m3 of PPF or CF delayed cracking by 23% and 18%, respectively. The results indicate that discrete CF can be potentially used to restrain the autogenous and drying shrinkage of cementitious materials.

Drying shrinkage is the major drawback of lightweight foamed concrete (LFC) as reported by many researchers. It is happened due to the loss of water in the capillary of concrete mixture. This problem caused the changes of dimension or volume of the concrete structure which lead to the cracking and failure thus shorten the life performance of the material. Once the water evaporated from the cement paste, it is impossible to replace it back. Thus, this paper studies the drying shrinkage behaviour of LFC with the confinement of woven fiberglass mesh at three different densities were 600kg/m3, 1100kg/m3, and 1600kg/m3. The woven fiberglass mesh implemented in this research is a synthetic textile fabric with an alkali resistance characteristic. The LFC specimens were wrapped 1-layer to 3-layer(s) of woven fiberglass mesh to enhance the drying shrinkage performance. The drying shrinkage test was measured accordance with the ASTM C157 specification and cured under air storage condition. Protein-based foaming agent (NORAITE PA-1) was used to produce the desirable density of LFC. The result shows that confinement of 160g of woven fiberglass mesh significantly improves the drying shrinkage of LFC compared to control and the enhancement also increase as the layer(s) of textile fabric is added from l-layer to 3-layer(s). Besides, the densities of LFC also play an important role to control its drying shrinkage behaviour. As proven at higher density of LFC the reduction of drying shrinkage value can be obtained.

With this research, the authors intend to investigate the effects of particle size and curing temperature on the properties of cement paste blended with iron tailings (IT). The research work found that the partial replacement of ordinary Portland cement (OPC) by iron tailings (IT) accelerated the hydration of cement in the initial stage, but low cumulative heat release was noticed after long curing. Both the yield stress and plastic viscosity of fresh cement paste blended with IT were decreased due to the IT replacement. The initial setting was found to be delayed by the addition of IT. Besides, the introduction of IT led to enhanced pore volume resulting in reduced UCS and the UCS decreased with the increase of IT particle size. On the other hand, the properties of cement in the presence of IT were found to be more temperature dependent. Increasing temperature accelerated the early-stage hydration of paste with IT more strongly than that of the control paste. Temperature rising was more favorable to the UCS development of samples with IT replacement. The grow rates of both yield stress and plastic viscosity increased due to the replacement of OPC by IT when the temperature rising.

This study evaluated and quantified the effect of nanoclay (NC) as an additive for the cement paste. Experimental tests and modeling and microstructure tests were conducted to predict the cement paste's flow properties such as yield stress, shear strength (shear stress limit), viscosity, and compression stress at the failure of cement after hardened. Two different rheological models were used to predict the rheological properties of the cement paste, and based on the statistical assessments, the Vipulanandan rheological model predicted the shear stress versus shear strain rate better than the P-E model. The nanoclay (NC)-modified cement paste was measured at 0.35 and 0.45 of water/cement ratios, and the temperature varied between 25 and 75 °C. NC has improved ultimate shear stress and yield stress, respectively, by 22.5%–54.4% and 26.3%–203% based on the NC content, water/cement ratio (w/c), and temperature. TGA tests have shown that 1% of nanoclay reduces the cement weight loss at 800 °C by 74% as a result of interaction with cement paste. Among the used approaches and based on the tested dataset, the model made according to the NLR models is the most reliable model to predict flow properties and compression strength of the cement and it is performing better than the ANN model according to statistical assessment such as coefficient of correlation (R) and root mean square error (RMSE).

In this work, different cementitious systems were used to investigate the shrinkage of concrete under plastic and drying conditions. Emphasis was placed on Portland limestone cement (type IL) with replacement amounts of 10% of Portland cement. Comparisons were made with a cement type with low Blaine fineness (i.e. coarse ground cement). The results indicated that type IL cement has good shrinkage results without adversely affecting other engineering properties of concrete such as strength, resistivity, degree of hydration and setting time. This is probably due to improved particle packing, access to more nucleation sites for the hydration products and the formation of calcium carbo-aluminate hydrates. Scanning electron micrographs of coarse ground cement paste also indicate a retarded degree of hydration compared to type I/II Portland cement paste.

The effect of polycarboxylate superplasticiser (PCS) architecture in terms of a flexible or rigid backbone and repartition of side-chains along the backbone on the hydrodynamic radius, adsorption properties, flow behaviour and rheological behaviour was systematically evaluated. PCSs with different architectures were found to affect the flow behaviour of cement paste differently, mainly due to difference in PCS surface coverage area on cement particle surfaces. The PCS surface coverage area on cement particle surfaces was determined by the adsorption layer thickness of a single PCS molecule and the adsorption amount. The adsorption layer thickness of a single PCS molecule is correlated with the hydrodynamic radius in solution. The PCS with a rigid structure in the main chain had a more coiled conformation, with an inevitably smaller hydrodynamic radius and thus a thinner adsorption layer. The adsorption amount is closely related to the exposed density of carboxylic groups. A more extended solution conformation facilitates the exposure of carboxylic groups, which is beneficial for the adsorption of PCS onto cement particle surfaces. As a consequence, the thicker the adsorption layer thickness of a single PCS molecule and a larger adsorption amount results in larger PCS surface coverage area on cement particle surfaces, producing better workability of cement paste.

Filling and nucleation are the mechanisms of modifying cement paste with nanomaterials, as investigated by previous studies, and are difficult to reflect the different effects of nanomaterials, especially on the changes of cement clinker and hydration products in the cement hydration process. In this study, the mechanisms of modifying cement paste with nano-calcium carbonate (NC), nano-graphene oxide (NG), nano-silica (NS), and nano-titanium dioxide (NT) were investigated by determining the mechanical properties of cement paste treated with nanomaterials and analysing the changes in the cement clinker (tricalcium silicate and dicalcium silicate), hydration products (portlandite and ettringite), and microstructure through many micro-test methods. The results indicate that the incorporation of nanomaterials could improve the early strength of cement paste specimens due to more consumption of cement clinker. Meanwhile, different nanomaterials promote the formation of different hydration products at early ages. C–A–S–H gel, flower-like ettringite, and C–S–H seeds are widely distributed in the cement paste with the incorporation of NC, NG, and NS, respectively. NT exhibits insignificant nucleation effect and has inhibitory effect on portlandite precipitation. This study provides key insights into the mechanism of nanomaterials from the perspective of cement hydration, which may promote the further research and application of nanomaterials in the cement and concrete industries.

These days, applications of nanotechnology in the field of construction are looking for a resolution to decrease the practice of cement and accordingly to decrease the discharge of pollutants in the environment. In this concern, the outcome of different proportions of the functionalized Multi - Walled Carbon Nanotubes (MWCNTs) on the alteration of mechanical properties of hardened cement paste and cubes was inspected. The addition percentages of Ordinary Portland Cement (OPC) & Portland Pozzolana Cement (PPC) with % replacement of MWCNT were 0%, 0.01%, 0.025% and 0.05%. Additionally, the Mechanical Property of the hardened Cement Concrete was inspected by the use of different tests on cement, aggregates, on fresh and hardened concrete. The concrete cube is tested in different temperatures (Room Temperature, High Temperature and Low Temperature) in this work. The results show that replacement of Ordinary Portland Cement (OPC) & Portland Pozzolana Cement (PPC) with up to 0.05% of the functionalized Carbon Nanotubes, as the optimum amount, can be considered both for enlightening mechanical properties with increase in strength up to 22% for OPC and 26% for PPC in different Temperatures (Room Temperature, High Temperature and Low Temperature).

Recently, as the construction of civil structures has increased, so has the demand for lightweight, high-strength structures. In the case of conventional lightweight cement composites, the unit volume weight can be lowered, but this leads to reduced strength. Generally, a lightweight composite can be created by mixing in a lightweight aggregate when combining cement composites. Various cement complexes use artificial lightweight aggregates, such as rubber aggregates and plastic pellets; of these, plastic sticks can secure the strength of the relatively high-strength aggregate, but the surface properties of the material make it disadvantageous to attach to the cement paste. In this study, cement composites using various types of plastic were produced and tested to determine the types of plastic most suitable as aggregates. The results confirm that the physical performance of the cement composites changes according to the specific gravity and/or surface of each plastic aggregate.

Nanosilica (NS) has shown significant beneficial effects on concrete. However, the utilization of NS to achieve its maximum benefits is limited by the agglomeration of nanoparticles, which is associated with production methods and the method of NS dispersion in concrete. In this study, the effects of the utilization of NS as a suspension in calcium hydroxide (CH) on the hydration characteristics and the microstructure of the cement pastes were investigated with different levels of cement replacements (1%, 2%, 4%, and 6% NS) at 2, 7, and 28 days. The hydration of the cement pastes was investigated by isothermal calorimetry, and the measurement of CH content by thermogravimetry. The microstructures were analyzed by scanning electron microscopy and by energy dispersive X-ray spectroscopic mapping. The microstructure of the pastes was characterized by analyzing the pore size and the pore size distribution using mercury intrusion porosimetry (MIP). The calorimetric studies indicated that the replacing cement by NS derived by this method leads to faster hydration up to 4% replacement. The CH contents could be reduced by the incorporation of NS. The pore structures revealed that the pastes with NS had become comparably denser than the pastes without NS. A positive insight into the durability characteristics was shown by the results of the MIP when using NS as suspensions.

The physio-chemical changes in concrete mixes due to different coarse aggregate (natural coarse aggregate and recycled coarse aggregate (RCA)) and mix design methods (conventional method and Particle Packing Method (PPM)) are studied using thermogravimetric analysis of the hydrated cement paste. A method is proposed to estimate the degree of hydration (α) from chemically bound water (WB). The PPM mix designed concrete mixes exhibit lower α. Recycled aggregate concrete (RAC) mixes exhibit higher and α after 7 d of curing, contrary to that after 28 and 90 d. The chemically bound water at infinite time (WB∞) of RAC mixes are lower than the respective conventional concrete mixes. The lower WB∞, Ca(OH)2 bound water, free Ca(OH)2 content and FT-IR analysis substantiate the use of pozzolanic cement in the parent concrete of RCA. The compressive strength of concrete and α cannot be correlated for concrete mixes with different aggregate type and mix design method as the present study confirms that the degree of hydration is not the only parameter which governs the macro-mechanical properties of concrete. In this regard, further study on the influence of interfacial transition zone, voids content and aggregate quality on macro-mechanical properties of concrete is needed.

The indirect tensile strength (ITS) of portland cement concrete (PCC) is commonly predicted using several existing empirical equations that relate this property to the compressive strength. Based o...

The rheology of cement paste under vibration follows the transformation from Bingham model to Hershel-Bulkly model to Power-Law model. Most of the existing research is obtained through a large number of experiments in the data fitting process, and cannot express the time-varying characteristics of viscosity. Furthermore, thixotropy of cement paste is based on static experiment and cannot be applied under vibration. In this paper a shear-vibration equivalent theory is proposed, which consider the effect of vibration is the same as the shear effect on the viscosity change of cement paste. Combining vibrational shear equivalent theory and HI theory, the rheological changes of cement paste under vibration are obtained through numerical simulation. This theory has been verified by a series of experiments with numerical simulations, and can be used to study the rheology of concrete under vibration.

Re-swelling capacity is a key factor influencing the self-sealing efficiency of superabsorbent polymers (SAPs) in concrete. In this paper, a new parameter (re-swelling ratio, η), the volume ratio of the crack which was filled with the expansive SAPs and the dry SAPs, was given to quantify the re-swelling capacity of a single SAPs particle. An innovative immersion test was used to study the η value of SAPs in the hardened cement paste with an artificial crack. Moreover, the influence of the crack width and particle size on the sealing efficiency of SAPs in the cracked paste was investigated by a water permeability test. The results showed that the mass ratios of the expansive SAPs in an artificial crack were less than those in a free state. The η value of SAPs in the hardened paste with an artificial crack increased with the increase of the crack width due to the restricting effects of the crack. The expansive SAPs in the cracked paste could totally seal or partly seal the crack within the original void. Moreover, the sealing efficiency of SAPs slightly increased with the rise of the crack width (0.25 to 0.5 mm) and the reduction of the particle size. This research demonstrates that the crack width in concrete and the particle size of SAPs are the key factors influencing the re-swelling behavior of SAPs which should be taken into consideration when designing the self-sealing concrete containing SAPs.

The restrained volume expansion of expansive agents during hydration is often used to offset strains caused by the shrinkage of cement-based materials (CBMs). The hydration and expansion process of a laboratory-prepared calcium-oxide (CaO)-type expansive agent (CEA) in CBMs and modelling of the same are discussed in this paper. Based on isothermal calorimetry and thermogravimetry/differential thermal analysis, the hydration behaviour of the CEA in cement paste was examined, based on which the hydration kinetics were analysed and the apparent hydration activation energy of the CEA was calculated. Based on the degree of hydration, a chemo-mechanical model of the expansion of the CEA in CBMs was developed and analysed by comparison with experimental data obtained by the dual-ring restraint test method. Based on this model, it is possible to predict the expansion performance and crack resistance of concrete containing CEA agent.

The compositions and contents of phases in cement paste soaked in sodium sulfate solution changing with time were investigated in this study. First of all, the porosities in cement paste specimens over time were measured by an in situ X-ray computed tomography (X-ray CT) test. Cement hydration and sulfate erosion occur simultaneously during the soaking process of cement paste specimens in sodium sulfate solution. Therefore, the hydration behaviour and the erosion of sulfates in cement paste were combined in a new way to establish an X-CT–hydration–deterioration model, which was used to calculate the variations of the volume fractions of the phases in cement paste. Subsequently, the volume fractions of each phase were used to calculate the elastic moduli of cement paste specimens with the bulk modulus, shear modulus of each phase and a self-consistent (SC) method. Afterward, the calculated elastic moduli were compared with the experimental results obtained by uniaxial compression test and the error values were 1% for 28 d, 2·5% for 88 d and 5% for 148 d, which were all within 5%, indicating that the advanced X-CT–hydration–deterioration model combined with the SC method can successfully predict the elastic modulus of cement paste eroded in sodium sulfate solution.

Nano-materials modified cement-based materials have attracted wide attention due to their advantages of improving strength and durability. In this paper, the effect of nano-SiO2 (NS) with particle sizes of 15 and 50 nm on the mechanical properties and microstructure of cement paste was studied. The results showed that 50 nm NS provided a greater compressive strength than that of 15 nm NS, while 15 nm NS afforded a denser microstructure than that of 50 nm NS. A fluctuation in the compressive strength was revealed using a physicochemical reaction equation, and the microstructure was interpreted by a pore structure analysis. In addition, the orientation index of calcium hydroxide (CH) with 15 nm NS could be reduced significantly in the early stages (the early stages refer to the first three days from the maintaining of specimens) compared with when the 50 nm NS was used. The experimental results also showed that NS helped increase the mechanical strength of cement paste, advance the endothermic peak of CH, and refine the size of the CH crystals. The microstructural changes at different stages of cement paste with different particle sizes of NS were investigated by X-ray diffraction, scanning electron microscopy, mercury intrusion porosimetry and differential thermal analysis. This study is expected to promote the research and application of nano-materials in the cement industry by clarifying the performance of NS with different particle sizes.

We introduced a parameter rs (the radius of the pores where the meniscus forms), which is composed of two factors, i e, water loss and cumulative pore size distribution (PSD), to provide a better explanation of the influence of superplasticizers(SPs) on early-age drying shrinkage. In our experiments, it is found that the addition of three types of SPs leads to a significant increase in the early-age drying shrinkage of cement paste, and drying shrinkage increases with the dosage of SPs. Based on the results above, we further studied the mechanism of the effects of SPs on the early-age drying shrinkage of cement paste by PSD and water loss, which are two components of rs. The experimental results indicate that rs can be a better index for the early-age drying shrinkage of cement-based materials with SPs than a single factor. In addition, the effects of SPs on other factors such as hydration degree and elastic modulus were also investigated and discussed.

Graphene oxide (GO) has attracted increasing attention for its application in cementitious materials as it can be used to regulate the hydration products of cement and improve the properties of cement composites. This paper investigated the role of GO on the hydration process and chemical shrinkage of a cement paste through an experimental study and molecular dynamics simulation. The hydration heat flow of a cement composite with GO (CCG) was characterised by using an isothermal calorimeter. The chemical shrinkage of the CCG was also measured by applying a modified method based on ASTM C1608. The test results have shown that incorporating GO can mainly accelerate the hydration rate of cement composites at the early stage, but would not change the four-stage process of the cement hydration. The addition of GO by 0.3 wt% of cement is able to reduce the chemical shrinkage of the cement composites. This regulation effect is mainly attributed to the hydrogen bonding, which has been verified by the molecular dynamics simulation.

The aims of this work are study the effects of adding nano zirconia ZrO2 particles (NZ) on the physical and some mechanical properties of cement paste like: porosity, dry density, water absorption and compressive strength, where different cement replacement weight percentages of NZ particles, 0%, 0.75%, 1.5%, 2.25%, and 3 % by weight of cement, had used in cement paste. Physical properties of the prepared specimens had been tested and evaluated after various curing times, 7, 14, 21, and 28 days, while compressive tests had been performed after 28 days. The results showed direct decreasing in porosity, water adsorption and increasing in density and compressive strength with increasing weight fractions of NZ. The maximum increasing in density and compressive strength were 13% and 21% respectively of that of plain cement paste, while porosity and water adsorption decreasing were about 43.5 % and 43.7 % respectively of that of plain cement paste, when using 2.25 wt. % NZ cement replacement, after curing for 28 days.

This paper discusses the effects of nano-silica (NS) particles with an average diameter of 15 and 50 nm on the hydration, setting time, compressive strength, drying process and microstructure of grey and white cement. The cement was partially substituted by 1·0 wt% of NS. The results show that NS was able to promote cement hydration and shorten the induction period determined by low-field nuclear magnetic resonance, and that the smaller the average particle size of NS, the shorter the setting time. The effect of NS on the improvement of compressive strength mainly manifested in the early stage (3 d). In addition, the introduction of NS with a diameter of 15 and 50 nm could reduce the water-loss rate of hardened samples during drying and decreased the porosity of the system. Furthermore, the content of calcium hydroxide was reduced by introducing NS particles measuring 15 and 50 nm in diameter. Finally, the addition of NS could refine the grain size and improve the morphology of calcium silicate hydrate gel.