Early Cement Hydration Research Articles

Effect of gypsum on the properties of composite binder containing high-volume slag and iron tailing powder

• Composite binder with high-volume slag and ITP shows low early compressive strength. • The addition of gypsum compensates for the poor early properties of composite binder. • The addition of gypsum negatively affects later-age properties of composite binder. • Adding gypsum increases Ca/Si ratio and S/Si ratio but doesn’t affect Al/Si ratio. • High-volume slag and ITP can be used to produce high performance green concrete. The effect of gypsum on the properties of composite binder containing high-volume slag and iron tailing powder was studied by measuring compressive strength, hydration heat, bound water content, hydration products, pore structure and morphology. The addition of gypsum increases early-age compressive strength and bound water content, but the opposite trend is observed at later ages. A higher quantity of gypsum leads to a higher third exothermic peak and a higher total hydration heat. Although incorporating gypsum promotes early hydration of cement and slag, it limits their further hydration at later ages. Adding gypsum forms a large amount of ettringite and densifies early-age pore structure, but it coarsens later-age pore structure. The addition of gypsum increases Ca/Si and S/Si ratios of C-S-H, but it doesn’t affect Al/Si ratio. The addition of gypsum compensates for the poor early-age properties of composite binder containing high-volume slag and iron tailing powder, and the later-age properties are acceptable.

Study of Fine-Grained Cementitious Composites in Solidification Phase Using Acoustic Testing Technique

The paper deals with experimental analysis, which is focused on the use of acoustic measurement during the solidification process. As a material for monitoring was chosen fine-grained cementitious composites in the laboratory environment. For this purpose, a measuring device working on the principle of mechanical waves passing through the material was designed, assembled and verified. The experiment was conducted on cement pastes prepared from CEM I 42.5 R Portland cement with two different water coefficients (w/c = 0.40 and w/c = 0.33). The differences in the wave propagation in cement pastes were investigated. Simultaneously with this experiment, the monitoring and the saving records of the internal temperature was conducted. The results show the time of „critical changes" in the internal structure of the material can be determined. These changes are probably related to the quality of the particle’s bonds in the inner material structure, which is reflected in the propagation of mechanical waves. Overall, it is shown these experiments could be used to expand the understanding of the various processes occurring during early hydration of cement, and the application of these results to field situations (in the future) could lead to the other development of, non-destructive (and nonintrusive) monitoring techniques.

Hydration process and microstructure evolution of low exothermic concrete produced with urea

In this paper, the feasibility of using urea as an additive to prepare low exothermic concrete is studied. The effect of different urea contents (0%, 5%, 10%, 15%) urea on the hydration process and the microstructure of the cementitious materials were investigated systematically. The experimental results show that urea has an obvious retarding effect on the early hydration of cement. The curve of the hydration heat release was significantly reduced and delayed with the urea content increased. The early strength of the concrete decreased significantly. Urea has almost no effect on the compressive strength of concrete at 28 days of age. The actual water-to-binder ratio is lowered, and the hygroscopicity and recrystallization of urea are the main reasons for shrinkage reduction and even micro-expansion of concrete. Scanning electron microscope (SEM) and X-ray diffractometer (XRD) results show that urea does not change the cement hydration products. The total amount of chemically bound water and the degree of hydration of the sample show that urea has a greater inhibitory effect on early hydration of cement and less effect on hydration in a later stage. The results of mercury intrusion porosimetry (MIP) show that the total porosity of cement paste has a consistent trend with mechanical properties. When the content of urea in concrete exceeds 10%, white crystals appear inside of concrete. The FourierTransformInfraredSpectrometry (FT-IR), Differential thermal analysis (TG-DSC) and SEM result show that crystalline product is produced by urea crystallization.

Influence of cement replacement by limestone calcined clay pozzolan on the engineering properties of mortar and concrete

This study investigates the effect of a new type of blended pozzolan on the hydration, mechanical and durability performance of cement. A blend of limestone calcined clay pozzolan (LCCP) was produced by grinding calcined clay and limestone in a ratio of 2 : 1 with 2% gypsum. Blends with cement replacement level of 0, 10, 15, 20, 30 and 50% using LCCP were cast. The effect of LCCP on the hydration of cement was investigated using isothermal calorimetry and X-ray diffraction. Mortar and concrete samples were cast to study the influence of LCCP on mechanical and transport properties. The addition of LCCP was found to have a beneficial effect on the early age hydration of cement. The induction period and initial setting time of cement paste were found to reduce on increased cement replacement level. Higher or similar compressive strength was observed for all the LCCP blends as compared to ordinary Portland cement. The pozzolanic reaction of calcined clay and formation of carboaluminates on the reaction of calcium carbonate with alumina helps to develop a refined pore structure that aids in reducing transport properties of concrete such as porosity, rate of water absorption and permeability.

Role of shear stress at rest on the viscoelastic response of fresh cement pastes

Fresh concrete is composed of aggregates and cement paste, which itself is a dense suspension that exhibits a yield stress and serves as a binder that solidifies through cement hydration. Although there is relatively little reaction during the fresh state (i.e., before setting), there is still the formation of early hydration products that will influence the paste rheology. Nonzero stress at rest widely exists in concrete practice, e.g., interruption during pumping, static formwork casting, and 3D concrete printing, but its impact on eventual viscoelastic properties is not well understood. In this study, we investigated the influence of different levels of applied shear stress at rest on fresh cement pastes and show that it dramatically alters the eventual solid performance (i.e., static yield stress and stiffness). With increasing applied shear stress at rest, the cement paste exhibited increasing static yield stress and increasingly elastic behavior, where the origin was tied to the progression of hydration. Cement pastes were compared against magnesium oxide suspensions, which served as an inert model system, and an accelerated rate of static yield stress increase over time was observed in the former but not in the latter. This highlights the role of early cement hydration on the solidification behavior of fresh cement pastes in the presence of nonzero shear stress at rest. We further support this by showing that the structural evolution of cement paste under applied stress can primarily be attributed to an enhanced elastic limit, which is associated with early hydration. The influence of two common viscosity modifying admixtures, nanoclay and diutan gum, on these properties was also examined. This work demonstrates the importance of taking the shear stress at rest into consideration for laboratory rheological experiments and industrial concrete applications, as it can substantially impact the eventual solidification behavior.

Pozzolanic activity of argentine vitreous breccia containing mordenite

A vitreous breccia with variable amount of mordenite was studied for its use as pozzolan. The raw material was characterized by optical and scanning electron microscopy (SEM), X-ray diffraction (XRD), and the zeolite content was estimated by the methylene blue staining technique. After being ground, physical characteristics, cation exchange capacity (CEC), pozzolanicity, and the compressive strength activity index (SAI) were determined. The staining technique and the CEC measurement were used to evaluate the average content of zeolite. The vitreous breccia has pozzolanic activity after 7 days, the water demand increases slightly, and its addition stimulates the early hydration of portland cement. At later ages, the pozzolanic reaction around the grains, as revealed by SEM studies, improves the compressive strength of blended cements having a SAI > 0.85 at 28 days.

Self-compacting mortars produced with fine fraction of calcined waste foundry sand (WFS) as alternative filler: Fresh-state, hydration and hardened-state properties

This work investigated the use of the <150 μm fraction of a calcined waste foundry sand (WFS) as filler in self-compacting mortars. WFS was calcined at 600–900 °C, referred to as calcined foundry sand (CFS). Self-compacting mortars were produced with cement replacement levels of 0–30 vol% with CFS and a limestone filler. WFS and CFS were characterized by X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectrometry (SEM-EDS) and thermogravimetric analysis (TGA). The fresh-state properties (mini slump flow and mini V-funnel), cement hydration (isothermal calorimetry and XRD), compressive strength and microstructure (SEM-EDS) of the mortars were evaluated. EDS showed that WFS calcination reduced its carbon content and XRD indicated the loss of the montmorillonite crystalline structure present in the clay material. CFS-containing mortars required superplasticizer contents from 2% to 10% higher than the reference to reach the target flow range (240–260 mm), while increased the mini V-funnel from 4.9 (reference) to 10.3 s (30% CFS). Nonetheless, all the mortars met EFNARC’s requirements. Calorimetry and XRD indicated that CFS enhanced the early age hydration of cement, increasing the main heat flow peak from 6.85 to 7.81 mW/g of cement and 72-h cumulative heat from 407 to 462 J/g of cement compared to limestone, with higher calcium hydroxide and lower alite contents at 3 days. CFS-containing mortars showed strength values about 14% higher than those containing limestone, for the same replacement level and age. Cement replacement with 10% CFS resulted in strengths equivalent to those of the reference mix at all ages (about 39, 45 and 54 MPa, respectively at 3, 7 and 28 days). SEM-EDS showed no significant differences between the microstructure of the mortars containing CFS and limestone. Overall, 10% CFS incorporation reduced 76 kg of cement and incorporated 58 kg of WFS per m³ of mortar, with equivalent performance.

Effect of sodium lignosulfonate superplasticizer on the early hydration of cement with different contents of cubic C3A

In this research, the influence of the sodium lignosulfonate superplasticizer (LS) on the early hydration of two types of cements containing different amount of cubic C3A was studied. It is shown that at 0.1% addition of LS has no significant influence on the hydration, while at higher dosages LS contributes to the additional formation of ettringite. This phenomenon is observed for both types of cement. The higher ettringite formation was found for the cement containing higher C3A amount. However, LS addition retards the hydration, which is indicated by the reduction of the portlandite amount formed.

Acceleration effect of synthesised calcium silicate hydrate with different morphologies and Ca/Si on cement hydration

Synthetic calcium silicate hydrate (C–S–H) is an important accelerator in cement chemistry. The early age hydration of cement was studied in the presence of synthetic C–S–H of different Ca/Si ratios and in different morphologies. Compressive strength, isothermal conduction calorimetry, zeta potential and inductively coupled plasma–optical emission spectroscopy were employed to investigate the acceleration efficiency. Results show that the extent of the acceleration was dependent on the amount, the morphologies and the chemical composition of the C–S–H, but not in a linear way; however, the acceleration efficiency was closely related to the specific surface area. It is suggested that the specific surface area is the main indicating factor for the acceleration efficiency. The induction period of cement hydration was shortened because the rate and the degree of dissolution of cement were increased while the secondary nucleation process energy of C–S–H was decreased. This paper provides an understanding of the effect of synthetic C–S–H of different Ca/Si ratios and morphologies on cement hydration and also sheds new light on the optimising effect of synthetic C–S–H on cement-based materials.

Enhanced slump retention using polycarboxylate superplasticizers obtained by micro-crosslinking reaction

In this paper, a facile method was adopted to synthesize polycarboxylate (PC) superplasticizers which rendered excellent initial fluidity and workability of mortar in 1 hour. Micro-crosslinking was introduced in the PC molecules and the ester groups in crosslinker can form carboxyl groups in the hydration solution of cement. The micro-crosslinked PC (MPC) superplasticizer was synthesized from butenyl alkylenepolyoxyethylene-polyoxypropylene ether, sodium methacrylate, acrylic acid with trimethylolpropane triacrylate (TMPTA) as the crosslinker in water medium. The effect of monomer content and the dosage of crosslinker on the performance of MPC were studied. Fourier transform infrared spectroscopy and dynamic light scattering analyses were conducted to characterize the molecular structure of MPC. The fluidity of mortar in 1 hour was tested to study the fluidity and the retention in fluidity of mortar with the presence of MPC, indicating that micro-crosslinking with trifunctional crosslinker TMPTA was an effective way to improve the fluidity retention without sacrificing the initial fluidity. Investigations on early hydration of cement with MPCs were performed using XRD and TGA. Results showed that the addition of MPCs can slightly improve the degree of early hydration.

Early hydration of CSA cement modified with styrene–butadiene copolymer dispersion

The effect of styrene–butadiene copolymer (SB) dispersion on the early hydration of calcium sulfoaluminate (CSA) cement was investigated. Pastes with five different ratios (0, 5, 10, 15 and 20%) of SB to CSA cement at a constant water to cement ratio of 0·4 were investigated by ultrasonic measurements, isothermal calorimetry, X-ray diffraction, thermogravimetry and scanning electron microscopy. It was found that SB retarded the initial hydration of the CSA cement paste within 3 h, during which time the formation of ettringite was strongly delayed. The hydration degree of the CSA cement paste was caught up by that of the SB-modified CSA cement paste at 3 h based on ultrasonic and calorimetry analysis. In addition, an increase in the addition of SB led to the generation of more ettringite and aluminium hydroxide. The most ettringite was formed and the size of ettringite crystals was increased in the pastes with 20% SB. Meanwhile, the addition of SB tended to reduce the amount of hemicarboaluminate in CSA cement pastes.

Characterization of the influence of Nanoparticles on Early Hydration of Oil Cement by Using Low Field NMR

ABSTRACT Based on the cement hydration theory and nucleation seeding, the nano-SiO2 and Al2O3 were introduced into the cement slurry system; then, the low-field nuclear magnetic resonance (NMR) was used to follow the cement hydration process and investigate the effect of the different nanometer materials directly comparable with each other. The relaxation peak location and peak area were used to further characterize the controlling effect of nanoparticles on the cement hydration. Meanwhile,the initial hydration process of the cement slurry systems was investigated by using the Carr–Purcell–Meiboom–Gill (CPMG) technique. As a result, it shows that the nano-SiO2 can accelerate the hydration of cement slurry, while nano-Al2O3 can retard the hydration of cement slurry system . Moreover, the change of compressive strength of cement stone was also studied, which found that the influence of nano-SiO2 and Al2O3 on cement hydration mainly focus on the initial hydration stage of cement, and the influence on the strength of cement stone in the later stage of hydration is very small.. The results of the current study show that the low-field NMR have great potential in exploring the effect of different nanoparticles on oil cement hydration.

Retardation effect of PCE superplasticizers with different architectures and their impacts on early strength of cement mortar

As the most effective superplasticizer, the comb-like PCE polymers also severely retard early cement hydration and hence decelerate early strength growth of concrete, which is undesired in some applications. In this study, a series of PCEs with different molecular architectures, including varied side chain length and density were synthetized by co-polymerizing acrylic acid and α-methallyl-ω-hydroxy poly(ethylene glycol) ether. Impacts of the obtained PCEs on cement hydration and early strength of mortar were investigated. Results show that adsorption of PCEs on cement grains is highly dependent on polymer architectures. Higher side chain length and density lead to lower adsorption amount and consequently higher early strength of mortar. It is interestingly found that the retardation effect of the PCEs on cement hydration is simply proportion to their absolute adsorption amounts on cement surface, while the complexation of R−COO− group with Ca2+, which is independent on polymer architectures, plays a minor role.

Effects of comb-like PCE and linear copolymers on workability and early hydration of a calcium sulfoaluminate belite cement

Fluidity control and setting adjustment are two critical issues for practical applications of calcium sulfoaluminate cement because of rapid hydration. A commonly used comb-like polycarboxylate superplasticizer (PCE) and linear copolymers (PAS) of acrylic acid (AA) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS) with varied monomer ratio were synthesized to study their impacts on fluidity and early hydration of calcium sulfoaluminate belite cement (CSAB). Results show that the linear PAS polymers are very effective in dispersing fresh cement pastes (fcps) and effectively inhibit early hydration of the cement. More AA unit in the PAS molecules leads to stronger inhibition effect on cement hydration. Compared with the PAS polymers, PCE exhibits almost no inhibition effect on cement hydration despite the high initial dispersibility. Thus, cement pastes containing PAS polymers exhibits excellent fluidity retention compared with the PCE containing fcp due to strong retardation effect of the PAS polymers on early formation of AFt crystals.

The effect of polymer dispersions on the early hydration of calcium sulfoaluminate cement

The influence of three polymer dispersions [styrene–butadiene copolymer (SB), styrene–acrylic ester copolymer (SA) and polyacrylic ester (PA)] on the hydration of calcium sulfoaluminate (CSA) cement within 72 h was investigated by using isothermal conduction calorimetry, X-ray diffraction analysis and thermal gravimetric analysis. The results indicate that these three polymer dispersions perform different influences on the hydration heat flow of CSA cement during different periods, they all postpone the occurrence time of the maxima peaks, and its extent is mainly dependent on the addition amount. Polymer dispersions manifest great retardation on the initial hydration of CSA cement, and the effect is much more significant within 1 h. In this stage, the generation of ettringite is strongly delayed; however, the formation of ettringite is accelerated by these polymer dispersions at and after 2 h. Among these three polymer dispersions, PA demonstrates the highest acceleration effect on the hydration degree.

Preparation of calcium silicate hydrate seeds by means of mechanochemical method and its effect on the early hydration of cement

Calcium silicate hydrate seeding is a promising accelerator for cement hydration. In this work, calcium silicate hydrate nanoparticles with various CaO/SiO2-ratios were prepared by means of mechano...

The effects of nano‐C‐S‐H with different polymer stabilizers on early cement hydration

AbstractA promising approach to accelerate cement hydration known as “seeding technology” has been discovered using nano‐particles to provide additional nucleation sites for growing of C‐S‐H. Two different types of polymer, polycarboxylate (PCE) and polysulfonate (PSE) were used as stabilizer to synthesize nano‐C‐S‐H via co‐precipitation process. The obtained C‐S‐H‐polymer composites were characterized by means of XRD, FTIR, thermogravimetric analysis (TGA), TEM, dynamic laser scattering (DLS), and BET. DLS measurement shows that the particle size of the obtained C‐S‐H‐polymer suspension ranges from 82.6 to 589.9 nm. The results of DLS and BET show that the particle size of the C‐S‐H particles synthesized using PCE polymer as stabilizer is smaller than those synthesized with PSE polymer, and hence the specific surface area is much higher. FTIR and TGA results confirm the presence of the polymers in the obtained C‐S‐H composites particles. XRD results indicate that the presence of the polymers reduces the crystallinity of C‐S‐H due to the absence of the d002 peak at 2θ of 7°. The calorimetry results show that the main hydration peak of cement is dramatically increased by the addition of the C‐S‐H‐polymer composites. It is interestingly found that the acceleration effect of the C‐S‐H‐polymer composites is linearly proportional to the total surface area of the nanoparticles introduced into the cement pastes. At the same time, it is found that the secondary hydration peak, usually known as the sulfate‐depletion peak, is greatly advanced by addition of the C‐S‐H nano‐particles in comparison with the blank cement paste. The acceleration effect of the nano‐C‐S‐H is further verified in a pure C3S system.

Hydration, Strength, and Shrinkage of Cementitious Materials Mixed with Simulated Desalination Brine

Abstract The process of desalination results in the production of a hypersaline waste by-product known as reject brine. In some locations, this reject brine is dumped back into the ocean, which has potentially detrimental effects on water quality and marine life. This study was carried out to investigate whether this brine could potentially be used to manufacture cementitious materials. The effects of different concentrations of simulated reject brine on hydration kinetics, compressive strength, and drying shrinkage of cement paste and mortar were investigated. Cement paste and mortars were prepared using a water-to-cement ratio of 0.45 and were mixed with simulated reject brine, tap water, and diluted reject brine (an equal mass mixture of reject brine and tap water). The results show that the reject brine causes an acceleration of early cement hydration; however, this effect is negligible at later ages. Mixtures containing reject brine have higher compressive strength at early ages, although this difference is reduced at 91 d. The reject brine causes a drastic increase in the drying shrinkage. The difference between the results obtained using reject brine and diluted reject brine were generally insignificant, which suggests that the effects of solution composition on the observed properties were not strong when solution concentrations were greater than a threshold value. Although these results are preliminary and further feasibility studies, including research on concrete durability, are required, the results suggest that reject brine may be used to make unreinforced concrete or concrete reinforced with noncorrosive materials.

Impact of Welan Gum on Cement Paste Containing PCE Superplasticizers with Different Charge Densities

AbstractAs a renewable materials, welan gum is microbial biopolymer which is fermented by bacteria. It is widely used in self‐compacting concrete because of its excellent rheological properties. After adding welan gum, the fluidity of cement will decrease rapidly. So it needs to be used together with superplasticizer. Two polycarboxylate superplasticizer with the acid/ether radio of 2 (PC‐2)and with the acid/ether radio of 6 (PC‐6)were synthesized. By FTIR measurements, carboxyl functional groups exists in the dialysed polymer. The specific anionic charge density measurement shows that PC‐6 provide more COO− than PC‐2 in alkaline solution. And TOC test analysis shows that the adsorbed amount of PC‐6 is higher than PC‐2 with low anionic charge density. PC‐6 with the higher COO− seems to be more affected by welan gum than PC‐2. From the rheological properties of cement paste mixed with PCEs and welan gum, it can be concluded that the addition of welan gum aggravates the trend of shear thickening. Hydration heat flow at different temperatures indicates the selected welan gum is capable of retarding early cement hydration even in high temperatures. Finally, the film forming property of the welan gum was initially studied through water loss rate test, and the film formation mechanism needs to be studied in the future.

Synthesis and performance of an environmentally friendly polycarboxylate superplasticizer based on modified poly(aspartic acid)

The environmentally friendly polycarboxylate superplasticizer based on modified poly(aspartic acid) (MPASPs) with varied grafting densities were prepared by partially ring-opening reaction of polysuccinimide (PSI) with polyetheramine M2005 (PEM) and sodium p-aminobenzenesulfonate (SPA) and subsequently hydrolyzing of the remaining imide ring under mildly alkaline conditions. FTIR was used to characterize the MPASPs. The properties of the MPASPs were evaluated by fluidity of cement paste, flexural strength of hardened cement mortar, adsorption amount on cement particle surface, zeta potential of cement paste, XRD and TG-DSC analysis. The results revealed that the MPASPs with proper incorporation of polyether side chains and benzene sulfonic acid groups could improve the fluidity of cement paste and the mechanical property of cement mortar. The fluidity of cement paste doped with MPASP-3 was 197% higher than that of PASP, and the cement mortar with MPASP-3 shown the highest flexural strength at both ages of 7 d and 28 d. The MPASPs could inhibit the early cement hydration while had little effect on later cement hydration. Based on the above results, the dispersion model of MPASPs in cement–water system was also discussed. This study offered a novel environmentally friendly superplasticizer based on a biodegradable green polymer and simple synthesis method.