Early-age Cement Paste Research Articles

Experimental research on aggregate restrained shrinkage and cracking of early-age cement paste

This study conducted mesoscale experimental research to investigate the effect of aggregate restraint on local deformation and cracking of early-age cement. The digital image correlation (DIC) method and a microscope were utilized to measure the deformation and cracking of the specimens. The principal strain was analyzed, and the effect of aggregate geometries and the interface transition zone (ITZ) on restrained shrinkage was discussed. Additionally, a cracking index was proposed to quantify the degree of cracking. The results reveal that aggregates without sharp edges lead to later cracking. Elliptical aggregates may offer weaker restraint than circular. The shrinkage at the corner is generally larger, and the direction changes more sharply. As the internal angle of the regular polygon increases, the deformation required for initial cracking increases. A linear relationship between the cracking index and cracking width is established, based on which quantitative analysis of the cracking degree can be conducted.

Early CO2 capturing mortar by incorporating a new potential carbide lime waste under controlled CO2 curing

Early-age cement paste or mortar can be enhanced by curing it in a CO2 chamber. The study was initiated with investigation on the optimum compressive strength by replacing cement to carbide lime with 0, 5, 10, 15 and 20% of Carbide Lime Waste (CLW) content. The desired CLW mortar at 28 normal curing age was selected and the similar mix proportion was again casted and the fresh CLW mortar was cured for 1,3 and 7 days under controlled CO2 curing. The CO2 concentration and temperature were fixed at 20% and 60% respectively. The compressive strength and depth of carbonation of CLW mortar was investigated. In addition, their microstructural properties under TGA test was analysed at the early curing ages by using cement pastes. It was found that the mortar containing 5% of CLW had the desired optimum compressive strength and UPV under water curing condition. Overall, the strength properties of control mortar and CLW mortar significantly enhanced at early strength gained by controlled CO2 curing as compared to the water curing technique. The used of 5% of CLW as the potential to substitute the cement portion has provide better understanding on CO2 sequestration in cement mortar. The microstructural result shows the CaCO3 precipitation in the CLW mortar was higher than the control mortar as CLW has Ca(OH)2 behaviour which effectively react with CO2 and formed stable CaCO3 precipitation in the mortar.

A generalized mixture rule for estimating the effective modulus of cement paste in early age

PurposeThe purpose of this paper is to obtain a theoretical model to analyze the effective modulus of cement paste in early age, including the setting and hardening periods, which has a great impact on mechanical properties of concrete structure.Design/methodology/approachBased on a power law approximation, a generalized mixture rule is used to construct the relationship between the effective modulus and hydration degree. In addition, a new model of the dependence of the Poisson's ratio on the hydration degree and water cement ratio is proposed for cement paste in early age.FindingsThe effective Young's modulus, storage shear modulus and Poisson's ratio of cement pastes with different water cement ratios and hydration degrees are studied by the presented model. The model can be applied to simulate the behavior of early-age cement paste at both the setting and the hardening periods. Compared with the experimental results, the correctness of the model is validated.Originality/valueThis work presents a mathematical model that can effectively estimate the effective Young's modulus and Poisson's ratio in the hardening period, and the storage shear modulus in the setting period of cement pastes.

Influence of CaO-based expansive agent, superabsorbent polymers and curing temperature on pore structure evolution of early-age cement paste

Influence of CaO-based expansive agent, superabsorbent polymers and curing temperature on pore structure evolution of early-age cement paste

Effect of alkoxysilane on early age hydration in portland cement pastes

Silanes added during mortar or concrete preparation, may modify the fresh state properties, hydration kinetics and mechanical strength of the final product. The effects of silanes on cement hydration have been widely studied in the literature, however, there is some controversy about its effect at short ages. The present study was undertaken to determine the effect of a TEOS-based alkoxysilane (UCA-T), produced by ultrasound-assisted pre-hydrolysis of an oligomeric precursor, on early age cement paste hydration. The nature of the processes modifying the various stages of cement hydration kinetics in the presence of the alkoxysilane was ascertained by analysing paste composition at several ages (defined on the grounds of calorimetric curve results) using XRD, TG-DTG, FTIR and Raman spectroscopy. The calorimetric curve of pastes containing UCA-T exhibited a new early age, pre-induction period exothermal peak, indicative of UCA-T hydrolysis, C3A and C3S dissolution and ettringite and C–S–H gel precipitation. Portlandite, however, did not precipitate but reacts with the Si(OH)4 sourced from UCA-T hydrolysis to generate further C–S–H gel. The induction period following on that new exothermal peak was considerably longer than the period observed in the reference cement, an effect that intensified at higher UCA-T content.

Effects of temperature rising inhibitor and shrinkage reducing admixture on pore structure of early-age cement paste

High-strength and high-performance concrete (HSHPC) is frequently used in practical engineering, but HSHPC tends to crack at an early age because of the large temperature drop (temperature shrinkage) and autogenous contraction. Therefore, a temperature rising inhibitor (TRI) and a shrinkage reducing admixture (SRA) are adopted to improve the properties of HSHPC. The macroproperties of concrete are closely linked to its pore structure. In this paper, the effects of the water-to-cement ratio (w/c) and TRI and SRA contents on the pore size distribution (PSD) and porosity of early-age cement paste were tested by low-field nuclear magnetic resonance spectroscopy (LF-NMR). The test results showed that the PSDs of samples generally contain two peaks. The most probable pore diameter (MPPD) increases with the w/c and reduces with the TRI content and age. However, the MPPD changes only slightly with SRA content. For the same SRA or TRI content, the MPPD changes in samples containing both SRA and TRI are similar to those of samples with TRI or SRA only. However, the combined use of SRA and TRI has an apparent influence on the PSDs of samples. The porosity becomes large with the w/c and SRA content but declines with TRI content. The porosities of samples with both SRA and TRI addition are significantly lower than those of samples without the SRA and/or TRI at 28 days. A modified two-peaks model, which is adapted from the Shimomura and Maekawa model, is developed for cement pastes with the TRI and/or SRA. The curves of the modified two-peaks model coincide with the experimental data.

Effect of Strain History and Mixture Proportions on Early-Age Cement Paste and Mortar Stress Relaxation

AbstractThe influence of sand particles, aging, and water–cement (w/c) ratio on the viscoelastic relaxation modulus of cement paste and mortars was measured at early ages (1–28 days). Furthermore, ...

Hydration and microstructural characterization of early-age cement paste with ultrasonic wave velocity and electrical resistivity measurements

Various non-destructive monitoring methods have been proposed to evaluate the early-age characteristics of cement paste, including the setting time and hardening, but the corresponding microstructural approach has not been reported in investigations of hydration products with non-destructive approaches. This study evaluates the microstructural evolution for 24 h in fresh cement paste through two types of non-destructive measurements, namely, ultrasonic wave velocity and electrical resistivity, compared with setting time by Vicat needle test. Observable non-destructive parameters can reflect the generated cement hydrates and change the tortuous path in the porous material including setting time, but the results of both methods provide different critical times of obtained parameters. To identify the formed hydration products at specific points, XRD and TG analyses are performed around the setting time. As a result, calcium hydroxide occurred after solid percolation mainly induces decreasing porosity and water depercolation, and these physicochemical changes were discussed with the measured non-destructive parameters.

A Simple yet Accurate Homogenization Method for Early Age Cement Pastes

A Simple yet Accurate Homogenization Method for Early Age Cement Pastes

Monitoring of acoustic emission behaviour during early-age cement paste hydration

Valuation of Portland cement hydration using non-destructive techniques at early age is of great interest for predicting its thermal and durability characteristics. The acoustic emission (AE) technique is verified to be a high-quality non-destructive tool for real-time monitoring of structural micro-changes during the lifetime of Cement-based material composites. In this study, AE was applied to study the relationship between recorded signal and mechanisms that were happened during cement paste hydration. By using AE sensors, Portland cement paste samples with w/c ratio of 0.33 and 0.4 were explored during the first 72 h of casting. The AE resulting signals in each stage of hydration were studied to describe the various mechanisms that were running throughout the hydration process.

Electrochemical cell design and impedance spectroscopy of cement hydration

Understanding the complexity of the chemical and microstructural evolution of cement during hydration remains a controversial subject, and although numerous techniques have been used to assess this process, further insight is still needed. Alternating current impedance spectroscopy has been demonstrated to be a sensitive and powerful technique for cement characterisation in both fresh and hardened states; however, it has also shown certain experimental limitations (e.g. data interpretation, electrode, and parasitic effects) that prevent its wider acceptance. This study assesses electrochemical cell design and the impedance response during cement hydration. The results show that a significant decrease in the parasitic effects at high frequencies (caused mainly by leads and electrode effects) can be achieved through an optimal cell design and impedance measurements correction, enabling correlation of impedance measurements to particular aspects of the cement hydration process. However, due the limited solid phase microstructural development and the high conductivity of cement paste at low degrees of hydration, the parasitic effects could not be fully eliminated for fresh or early-age cement pastes.

CO2 Curing Efficiency for Cement Paste and Mortars Produced by a Low Water-to-Cement Ratio.

Curing by CO2 is a way to utilize CO2 to reduce greenhouse gas emissions. Placing early-age cement paste in a CO2 chamber or pressure vessel accelerates its strength development. Cement carbonation is attributed to the quickened strength development, and CO2 uptake can be quantitatively evaluated by measuring CO2 gas pressure loss in the pressure vessel. A decrease in CO2 gas pressure is observed with all cement pastes and mortar samples regardless of the mix proportion and the casting method; one method involves compacting a low water-to-cement ratio mix, and the other method comprises a normal mix consolidated in a mold. The efficiency of the CO2 curing is superior when a 20% concentration of CO2 gas is supplied at a relative humidity of 75%. CO2 uptake in specimens with the same CO2 curing condition is different for each specimen size. As the specimen scale is larger, the depth of carbonation is smaller. Incorporating colloidal silica enhances the carbonation as well as the hydration of cement, which results in contributing to the increase in the 28-day strength.

Role of Limestone Powder in Early-Age Cement Paste Considering Fineness Effects

AbstractThis paper investigates the influence of limestone powder (LS) fineness on the early-age properties of portland cement paste. Blended pastes with LS were prepared based on volumetric ratio ...

A Mathematical Model for the Electrical Resistivity of Cement Paste at Early Ages Considering the Partially Saturated State.

For cementitious materials, electrical resistivity is often used in the study of the cement hydration process at early age, as one of the few indicators that can be continuously and non-destructively monitored. Variation characteristics of resistivity are widely reported to interact with the early-age performance of cement paste, such as hydration kinetics parameters and setting time. However, there is no reasonable mathematical model to predict the resistivity at early ages, especially within the first 24 h, due to significant changes in the porosity and degree of saturation. In this work, a mathematical model was developed by considering the partially saturated state and density change of C-S-H (calcium silicate hydrate). To verify the model, two experimental methods were chosen, including the non-contact electrical resistivity test and isothermal calorimetry test. The hydration heat and resistivity of cement paste with a water–cement ratio of 0.35 and 0.45 were continuously monitored for 3 days. In the resistivity test, embedded temperature sensors were used to monitor the internal temperature and temperature correction was treated carefully in order to obtain accurate data. The test results prove that the mathematical model can accurately predict electrical resistivity and describe the saturation state of early-age cement pastes under sealed curing.

Investigation of thermal conductivity and related parameters of early-age cement paste

Thermal conductivity (TC) of cement-based materials is a key parameter for temperature field analysis and crack control at early age. In this study, the TC of early-age cement paste was experimentally determined by the parallel hot wire technique. The test results showed that the TC of early-age cement paste changed obviously with age and water to cement ratio (w/c). The TC curves of cement pastes with different w/c were similar and could be divided into three stages, i.e., the curves first rapidly decreased, then sharply increased, and finally tended to stabilize. The TC of the cement paste almost linearly decreased with w/c after 40 hours. Meanwhile, based on a combined generalized self-consistent method with CEMHYD3D, an effective TC multiscale predictive model for early-age cement paste was proposed considering the thermal resistance. An improved inversion program was simultaneously developed based on the particle swarm optimization. The TC of each phase in cement paste and the parameters of thermal resistance were obtained using the inversion program with experimental data. The inversion results showed that the deviations of the TC of each phase and the parameters of thermal resistance with different w/c were minimal and that the algorithm of the inversion program proposed was robust. The TC multiscale model predictive curves were in good agreement with the test data and the predictive capability of the TC multiscale model for cement paste was successfully validated.

Upcycling waste seashells with cement: Rheology and early-age properties of Portland cement paste

To reduce solid waste discharges into environment and virgin resource consumptions in construction, waste seashells from seafood and aquaculture industry were recycled into powder form and reused in cementitious construction materials. This work aimed to use this biologically renewable waste material as a possible alternative to the nonrenewable limestone mineral used conventionally with Portland cement. The study explored roles of seashell powder as both a partial replacement and an additional additive to cement through evaluating the rheological and physico-mechanical properties of early-age cement paste. The cyclic rheological measurement including model analysis (Bingham, Casson, and Herschel-Bulkley models) was conducted to reveal the time- and shear-dependent workability of fresh cement paste during the first 2 h. Connecting to rheology, physico-mechanical measurements were carried out to understand hydration mechanisms of cement paste with seashell powder. Seashell powder was found to improve the rheological and early hydration behaviors of Portland cement paste. A parallel comparison between limestone and seashell powders was conducted to understand different roles of the two calcium carbonate minerals in cement system. Results from this study indicated the unique physical features and chemical reactivities of seashell powder in cement system, and thus suggested a promising feasibility to recycle waste seashells with cementitious construction materials.

Effects of curing temperature and superabsorbent polymers on hydration of early-age cement paste containing a CaO-based expansive additive

The early-age shrinkage can easily result in crack of concrete in the early age, which seriously affects the durability of concrete. The CaO-based expansion additive is a normally used and effective material for the shrinkage compensation and the reduction of early-age crack risk in concrete. The hydration is a factor that significantly influences the mechanical and durability properties of concrete, and the study on the hydration of the cement paste containing a CaO-based expansive additive under different curing temperature and with superabsorbent polymers addition is lacking. In this study, tests were conducted using the low-field nuclear magnetic resonance to assess the effect of curing temperature and superabsorbent polymers on the hydration of early-age cement paste containing a CaO-based expansion additive. The experimental results show that the incorporation of CaO-based expansive additive can promote the hydration of cement paste, and 2% dosage of CaO-based expansive additive has a better promotion than that of 3% dosage. High curing temperature can effectively accelerate the hydration of cement paste containing the CaO-based expansion additive. In addition, superabsorbent polymers can also effectively promote hydration.

Hydration of Early Age Cement Paste with Nano-CaCO3 and SAP by LF-NMR Spectroscopy: Mechanism and Prediction

In this paper, by testing the evolution of the physically bound water using the low-field nuclear magnetic resonance (LF-NMR) technology, the hydration process of cement paste with nano-CaCO3 (NC) and superabsorbent polymer (SAP) at early age is investigated. Results indicate that the hydration process can be divided into four periods according to the zero points of the second-order differential hydration curve: initial period, acceleration period, deceleration period, and steady period. Firstly, with the increase in the water to cement ratio, the starting time of the hydration period is delayed, and the duration becomes longer. Secondly, the addition of NC leads to the speedy arrival of each period and shortens the duration of each period in the hydration process, and the optimal NC content is 1.5%. Thirdly, with the increase in SAP content, the starting time of the hydration period is delayed and the duration becomes longer. Finally, based on the experimental results and the existing hydration model, the modified hydration model considering the content of NC and SAP is proposed.

Experimental investigation of the early-age mechanical behaviour of oil-well cement paste

The knowledge of the behaviour of oil-well cement paste from the early age to the hardened state is important in predicting the performances of the cement sheath in oil/gas wells, specially for prediction of the risk of micro-annulus creation between the cement sheath and the rock formation or the casing. Characterization of the early-age mechanical behaviour is of particular importance, because during the well construction, the cement sheath is submitted to various mechanical loadings when the cement paste is not completely hydrated, as for example during a casing test. In this paper, the early-age mechanical behaviour of a class G cement paste is studied experimentally. A specially designed experimental device is used to investigate the mechanical behaviour of cement paste from the first hour of hydration, under stress states close to in-situ conditions. The macroscopic shrinkage of the cement paste as well as its stress-strain response under oedometric loading are studied for various pressures during hydration, from 0.3 to 45 MPa, and for hydration temperatures from 7 to 30 °C. These relatively low temperatures are used to slow down the hydration rate. The experimental results show that the macroscopic shrinkage increases significantly with the pressure during hydration. When submitted to a mechanical loading cycles at a given age, the cement paste hydrated under lower pressures, corresponding to shallower depth, exhibits higher deformability, showing a higher risk of creation of a micro-annulus during the mechanical loadings, as for example during a casing test. The experimental results clearly show the influence of the loading history on the mechanical behaviour of the cement paste at a given age. The oedometric experiments are associated with UCA (Ultrasonic Cement Analyser) and isothermal calorimetry experiments for a deeper insight into the behaviour of early age cement paste.

Pore structure characterization of early-age cement pastes blended with high-volume fly ash

High-volume fly ash is normally used as a partial replacement for cement to improve the workability, durability, and economic properties of concrete. The pore structure is an important factor affecting the performance of concrete. In this study, the influence of water-binder ratio (w/b) and fly ash content on the pore structure of early-age cement paste was determined using low-field nuclear magnetic resonance spectroscopy. Experimental results show that the most probable pore diameter increases with fly ash content and w/b and decreases with age. The porosity increases with w/b and decreases with age. A modified pore structure model, which is based on the existing models and the Weiball distribution, is proposed for high-volume fly ash cement-based materials.