Hydration Mechanism Of Cement Research Articles

Influence of the wide range cement content on the properties of cement–treated marine soft soil and bound method of semi–solidified soil

In order to identify the upper and lower boundary cement content for modified marine soft soil (i.e., semi–solidified soils), physical, compaction, and unconfined compressive strength tests of cement–treated soils with a wide range of cement content were carried out to study their variation law of physical–compaction–mechanical properties. The test results show that cement–treated soil can be divided into uselessly treated soil, semi–solidified soil, and solidified soil with the increase of cement content. For uselessly treated soil, the treated soil cannot be compacted even after compaction delay. Cement hydration in semi–solidified soil significantly improved its physical and compaction properties. However, compaction destroyed the skeleton structure of solidified soil, resulting in lower strength than compacted semi–solidified soil. Based on the cement–soil particles–water relationship, soil particles–water transfer mechanism, cement hydration mechanism and the state of soil particles–water before and after treated, the bound method of semi–solidified soils based on cement content and moisture content ratio of untreated soil was established. The test parameters of bound method are simple, easily obtained and have small dispersion, which provides design basis and theoretical support for resource utilization of marine soft soil.

Tailored rheological development in OPC systems by controlled ettringite precipitation and its effect on compressive strength

AbstractThe control of rheological properties is gaining in importance to meet the special requirements for cementitious materials in novel technologies such as 3D‐printing. A deeper understanding of the underlying mechanisms of cement hydration is necessary to customize the mix design to the specific application.The hydration of OPC is mainly characterized by the silicate and aluminate reaction. The aluminate reaction is especially relevant for the early rheological development, whereas the formation of C‐S‐H (silicate reaction) is responsible for the later hardening of the hydrating paste.A hydration control agent is used to delay the initial aluminate reaction to a defined point in time. When no additional mixing occurs during this period of rapid ettringite precipitation, the cement paste stiffens to a solid cement stone. However, when the sample is mixed during this period, the workability of the paste is retained. The rheological changes can be correlated directly to the magnitude of ettringite formation. Additionally, the compressive strength and pore size distribution of all systems (reference, HCA, HCA with additional mixing) are investigated to analyze the long‐term properties. These results predict future customized mix designs in various application fields.

Atomic-Level and Surface Structure of Calcium Silicate Hydrate Nanofoils.

Deciphering the calcium silicate hydrate (C-S-H) surface is crucial for unraveling the mechanisms of cement hydration and property development. Experimental observations of C-S-H in cement systems suggest a surface termination which is fundamentally different from the silicate-terminated surface assumed in many atomistic level studies. Here, a new multiparameter approach to describing the (001) basal C-S-H surface is developed, which considers how the surface termination affects the overall properties (Ca/Si ratio, mean chain length, relative concentration of silanol and hydroxide groups). Contrary to current beliefs, it is concluded that the (001) C-S-H surface is dominantly calcium terminated. Finally, an adsorption mechanism for calcium and hydroxide ions is proposed, which is in agreement with the surface charge densities observed in previous studies.

Effect of the incorporation of an excavated earth fine grained fraction in cementitious mixes

In the current context of global warming, valorisation of waste materials is becoming a key issue in the cement and concrete industries. This research focuses on the effect of the incorporation of an excavated earth fine-grained fraction (< 63 μm) in cement mixes and its contribution to the cement hydration mechanisms which are mainly coming from the Paris region of France. This fine-grained fraction results from a washing and mechanical sorting of grains process for excavated earth. The omnipresence of gypsum in the subsoil of the Paris region, due to its geological context, is reflected in the fine-grained fraction with the presence of sulphates. Moreover, the fine-grained fraction is also composed of quartz, calcium carbonates and clay phases. The tests have been performed on cement pastes composed of a blast furnace slag cement and the fine-grained fraction as a sludge with its inherent humidity. Pastes with different sludge contents leading to different water-cement ratios (0.5, 0.7 and 0.8) have been studied. The impact of the incorporation of the fine particles and the water contained in the sludge on the rheology and the hydration of the cement pastes has been evaluated using water demand tests, thermogravimetric analysis and isothermal calorimetry. Results indicate that the incorporation of sludge in cementitious mixes increases the water demand, accelerates the hydration reactions and contributes to the formation of additional hydrate phases probably associated with the presence of gypsum in the studied sludge.

Dissolution–precipitation kinetics during C[formula omitted]S hydration: A holographic interferometry study

Tricalcium silicate C3S has been widely employed in model systems to interpret the complex mechanisms of cement hydration. The present study aims at providing an accurate description of the dissolution rate of C3S by implementing a new approach based on holographic interferometry. We propose a protocol that allows the measurement of the pure dissolution rate constant of the C3S phase by experiments performed in supersaturated conditions with respect to C–S–H. In these experiments, a flat polycrystalline surface of C3S was monitored in a quiescent solution. The amount of calcium released within the holographic cell was measured and the aqueous solution composition was constrained to the C–S–H stoichiometry at the interface. An equilibrium approach was applied to assess interfacial pH, saturation indexes, and C–S–H precipitation at the experimental conditions. The rate law of the pure dissolution of C3S was assessed in conditions ranging from far to close-to-equilibrium.

The time-dependent grout buoyancy behavior based on cement hydration mechanism

The grout buoyancy has a great influence on the segment during synchronous grouting of shield tunnel. Traditionally, the large buoyancy leads to certain types of tunnel distresses, such as convergence deformation, differential settlement, cracks, and water leakage. This paper made a detailed study on the time-dependent grout buoyancy behavior. The hydration heat test and LF-NMR test were carried out. Then the four periods of hydration rate curve were revealed, and the evolution rules of gel water, capillary water and free water were also obtained. The time-dependent grout buoyancy was tested by self-designed equipment, and the theoretical formula of grout buoyancy considering w/c ratio and time was proposed. The indoor test results were compared with the theoretical solution. The theoretical formulas could effectively predict the size and variation rules of buoyancy. The indoor test results showed that variation trend of cement grout buoyancy is consistent with the hydration rules. The buoyancy mainly exists in the initial period and the induction period, and decreases sharply to zero before the acceleration period. The initial setting moment is the one in which hydration rate is the largest.

Alkali -silica reaction and its dynamic relationship with cement pore solution in highly reactive systems

Despite extensive research, the relationship between the progression of alkali-silica reaction (ASR) and the cement hydration mechanism, particularly the influence of the pore solution composition on the nature of reaction products is not thoroughly understood. A multi-analytical approach was applied to study ASR mechanism under accelerated conditions using a mortar system comprising of fused silica aggregates. For the first time, large field SEM mapping was used to correlate physical expansion with the composition, distribution and amount of ASR reaction products produced over time. A three-stage behavioral model was proposed to explain the dynamic relationship between ASR progression and pore solution composition. The results confirmed the co-existence of two phases within the ASR products: a CSH- type gel and an ASR-type gel. The relative abundance of one gel type over the other was dictated by their accessibility to the pore solution, which in turn influences how ASR propagates through the microstructure.

Retardation mechanism of cement hydration by a comb polyphosphate superplasticizer

Schematic presentation of the interaction between model cement and directly added polycarboxylate and polyphosphate superplasticizers. • At low doses, polyphosphate SP inhibits silicate reaction without affecting aluminate reaction and formation of ettringite. • At high doses, polyphosphate SP retards silicate and aluminate reactions, which follows by acceleration of both reactions. • Polyphosphate SP has higher affinity to C 3 S compared to PCE. • Retardation induced by direct addition of polyphosphate SP is similar to retardation induced by delayed addition of PCE. The retardation mechanism of cement hydration as imparted by the addition of polyphosphate comb superplasticizer to model cement containing C 3 S, C 3 A and calcium sulfate hemihydrate is studied using XRD, ss NMR and calorimetry. Our findings show the retardation effect caused by the direct addition of polyphosphate comb superplasticizer differs significantly to that of conventional polycarboxylate superplasticizers. Conversely to polycarboxylates, polyphosphates, at a low dosage, inhibits the silicate reaction without affecting the aluminate reaction and formation of ettringite. Yet, at high doses, both reactions are hampered, and the induction period extended, followed by accelerated aluminate and silicate reactions.

ASSESSMENT OF THE EFFECT OF MODIFIED ADDITIVES ON THE HOMOGENEITY OF AERATED CONCRETE BY LABORATORY TESTS

Three methods for obtaining non-firing lightweight materials based on wood-working waste, while suggesting ways to utilize woodworking waste into a light aggregate, optimal compositions of modifying bonding agents and the mechanism of cement hydration in the presence of dispersed polymer powders are taken into account in the given article.

Numerical study on microscale and macroscale strength behaviors of hardening cemented paste backfill

Computer aided optimization of cement-based materials proportion can accurately quantify the accompanying microstructure evolution, material composition, and the mechanical properties changes. However, no relevant research exists on the effect of cement hydration on cemented paste backfill (CPB) strength using numerical simulation considering above mentioned aspects. This study builds a numerical model based on continuous damage mechanics methods considering CPB hardening process per the particle size distribution (PSD) of tailings, the known determined strength characteristics of components, and the existing cognition of cement hydration mechanism. A series of CPB mechanical properties simulation was then carried out. The relations and influencing factors between CPB’s hardening process and mechanical parameters were obtained. Results have showed that numerical simulation can more intuitively show the relationship between the crack development and PSD of CPB’s hardening process at different stages under external load, and can quantitatively analyze the influence of strength properties. The strength development during CPB hardening is the combined result of matric suction and hydration products. The smaller the solid content, the more prominent the matric suction during hardening. The greater the binder content, the less the effect of matric suction on strength. The binding ability of cement hydration products to tailing particles is linked with the spatial distribution of tailing particles. The tailings gradation plays a key role on CPB’s strength characteristics. The heterogeneous distribution of CPB strength can be configured by analyzing the non-uniform distribution of hydration degree in CPB’s hardening mechanism. Accordingly, the proposed framework can not only provide theoretical guidance for the preparation and application of CPB, but also can save the cost and interminable time of laboratory tests and reduce the uncertain factors caused by environmental conditions.

A Novel Strength Model for Cement Marine Clay Based on the Mechanical-Chemical Coupling Behavior

Crucial mechanical-chemical (MC) interactions occur during the cement hydration process in cement marine clay; however, the role of such an important element of the resulting strength has been subject to less investigation, particularly from the theoretical perspective. To overcome this scientific gap, an efficient strength-based model accounting for the coupled MC processes is proposed here. Based on the analysis of the cement hydration mechanism, the porosity was chosen as the main factor to characterize the influence of the MC interactions on the overall response. To verify the accuracy of the MC model, the unconfined compressive strength (UCS) experiment was conducted for the cement marine clay samples, and the corresponding simulation model was constructed using COMSOL multiphysics®. In addition, a comparison between the predicted results by the existing three strength models and the proposed MC model was performed. Subsequently, the sensitivity analysis and identification of mechanical parameters were carefully carried out. The obtained results show that the UCS strength for Taizhou clay ranges from 10.21 kPa to 354.2 kPa as the cement content increases from 10% to 20%, and the curing time varies from 3 days to 28 days. The mechanical parameters in the MC model can be obtained according to the porosity level. A reasonably good agreement between the UCS strength results of simulations and the experimentally observed data is reported. Additionally, the predicted UCS strength results by the MC model demonstrate the best correspondence with the measured values, indicating the high efficacy of the established model.

The effect and mechanism of C–S–H-PCE nanocomposites on the early strength of mortar under different water-to-cement ratio

C–S–H-PCE nanocomposites (CPNs) serving as nucleation sites are a promising material to accelerate the cement hydration and gain high early strength for cementitious materials. This study aimed to investigate the effects of CPNs on the properties and hydration of cement mortar under different water-to-cement (w/c) ratios. CPNs were prepared via the co-precipitation method in MAPEG-PCE solution and characterized by means of XRD, FT-IR, DLS, TEM, TGA, and TOC. The mechanism and effect of CPNs on the early hydration of cement mortar with w/c ratios of 0.50, 0.40, and 0.35 were assessed in terms of mechanical properties, isothermal calorimetry, setting time XRD, TGA, SEM, and MIP. The results showed that CPNs significantly promoted the early strength development of mortar and a higher enhancement ratio was brought at a lower w/c ratio. Calorimetry and setting results also showed a greater hydration acceleration of samples dosed CPNs with lower w/c ratio. From the analysis of XRD and TGA, the content of CH and C–S–H in the samples dosed CPNs increased with the decrease of w/c ratio in 6 h, while exhibited an opposite trend in 12 h and 3 d. MIP and SEM results showed that CPNs led to a refinement of pore structure and dense morphology, especially at a low w/c ratio. Moreover, the underlying acceleration mechanism of cement hydration versus w/c ratio was that the seeding ability was enhanced for the low distance between cement and CPNs at a low w/c ratio. According to this research, the use of CPNs may be more practical in high-strength concrete.

Effect of C-S-H Nucleating Agent on Cement Hydration

This work aims to study the effect of a nucleating agent on cement hydration. Firstly, the C-S-H crystal nucleation early strength agent (CNA) is prepared. Then, the effects of CNA on cement hydration mechanism, early strength enhancement effect, C-S-H content, 28-days hydration degree and 28-days fractal dimension of hydration products are studied by hydration kinetics calculation, resistivity test, BET specific surface area test and quantitative analysis of backscattered electron (BSE) images, respectively. The results show that CNA significantly improves the hydration degree of cement mixture, which is better than triethanolamine (TEA). CNA shortens the beginning time of the induction period by 49.3 min and the end time of the cement hydration acceleration period by 105.1 min than the blank sample. CNA increases the fractal dimension of hydration products, while TEA decreases the fractal dimension. CNA significantly improves the early strength of cement mortars; the 1-day and 3-days strength of cement mortars with CNA are more than the 3-days and 7-days strength of the blank sample. These results will provide a reference for the practical application of the C-S-H nucleating agent.

A dissolution model of alite coupling surface topography and ions transport under different hydrodynamics conditions at microscale

Portland cement is the most produced material in the world. The hydration process of cement consists of a group of complex chemical reactions. In order to investigate the mechanism of cement hydration, it is vital to study the hydration of each phase separately. An integrated model is proposed in this paper to simulate the dissolution of alite under different hydrodynamic conditions at microscale, coupling Kinetic Monte Carlo model (KMC), Lattice Boltzmann method (LBM) and diffusion boundary layer (DBL). The dissolution of alite is initialised with KMC. Two Multiple-relaxation-time (MRT) LB models are used to simulate the fluid flow and transport of ions, respectively. For solid-liquid interface, DBL is adapted to calculate the concentration gradient and dissolution flux. The model is validated with experiment from literature. The simulation results show good agreements with the results published in the literature.

New insights into the effects of aging on Portland cement hydration and on retarder performance

To gain a better understanding of the aging impact on the mechanisms of cement hydration, a Portland cement was intentionally exposed to moist air under controlled conditions. This resulted in the formation of nanoscale ettringite needles on the particle surfaces which act as seeding materials, thereby accelerating setting. The subsequent ettringite overgrowth of cement particles slows water access to the silicate phases, thus retarding strength development. The effectiveness of gluconate and pyrophosphate retarders against this accelerated hydration is limited at short aging periods, but sharply increases towards prolonged aging times when the ettringite seeds are carbonated by atmospheric CO2.

Negative effect of zinc compounds on hydration kinetics of ordinary Portland cement

Metals and metal containing compounds have significant effect on cement hydration mechanism and kinetics. The recycling of waste materials leads to increase of content of metals in various industrial products and visibly affects properties of the Portland cement. One of the metals that has been known to drastically increase the setting time is zinc. Zinc forms various hydroxyl species with calcium cations. Pore solution thus has lowered concentration of calcium which suppresses formation of portlandite. Due to insufficient concentration of calcium the formation of CSH gel and further hydration of clinker grains is inhibited The aim of this study is to quantify the negative effects of zinc at different concentrations at ambient temperature at 20°C. Isoperibolic calorimetry was used to measure the negative effects of zinc on hydration kinetics of ordinary Portland cement. Zinc was added to the cement in the form of two soluble salts Zn(NO3)2 hydrate, ZnCl2 and a poorly soluble compound ZnO. The concentration of zinc added was chosen between 0.1 and 1 wt. % of clinker. Significant retardation of cement hydration with increasing zinc content was proven.

Lightweight materials based on wood waste

This paper discusses ways of recycling woodworking waste into light aggregate, optimal compositions of modified binders, as well as the mechanism of cement hydration in the presence of dispersion polymer powders. The methods of obtaining light aggregate based on woodworking waste by granulating in a disc granulator, which is a plate with a tilt angle of 450 and a number of turnovers of 17-19 rpm, are considered. Methods for obtaining granulated aggregate using sawdust of various fractions by the roasting free method are presented, optimal granulation modes are determined, and the main characteristics of the resulting aggregate and concrete based on them are studied. The optimal composition of granulated aggregate on modified cement provides 40 … 60 % of wood processing waste, 60 … 40 % of cement, 25 … 32 % of water and granulation time - 7 … 9 minutes. With this composition, the bulk density of the resulting aggregate corresponds to 850…750 kg/m3, the maximum strength of the granules when compressed in the cylinder is 3.5…4.1 MPa. The optimal content of the polymer additive in the binder is in the range of: mowilith - 0.4…0.7 % and tylose - 0.21…0.13 %. Granulated aggregate on modified aggregate has a frost resistance in the range of F35… F50. The choice of granulated aggregate on modified cement showed the effectiveness of the aggregate for light concretes. The strength characteristics of modified concrete of 25-75 brands were studied. The mechanical properties of modified concrete depending on the average density were studied. Concrete with an average density of 1000 kg/m3 has M25 brand, at 1200 kg/m3 - M35, at 1300 kg/m3 - M50, at 1500 kg/m3 - M75.

Measuring and modeling cement hydration kinetics at variable temperature conditions

The heat evolution during the hydration of a Class H oil well cement was examined by both the traditional isothermal calorimetry method and a new differential scanning calorimetry (DSC) method. Isothermal calorimetry tests were performed at four different temperatures: 15, 25, 40, and 60 °C. DSC tests were performed in two different modes: simple ramp mode in the temperature range from 24 to 100 °C, as well as “ramp and hold” mode, with final holding temperatures of 60, 80 and 260 °C, respectively. The ramp rate ranged from 0.3 to 4.8 °C/h. A scale factor model previous proposed to simulate cement hydration kinetics at isothermal conditions was further developed into a numerical format to simulate cement hydration at variable temperature conditions. Excellent agreements were observed between experimental and simulated results. The study not only provided a new method of measuring cement hydration kinetics but also further advanced our understanding of cement hydration mechanism.

Study on the early cement hydration process in the presence of cationic asphalt emulsion

Cement-asphalt (CA) paste could be regarded as the Portland cement (PC) paste with enhanced flexibility due to the addition of asphalt emulsion (AE) and could be utilized as the semi-flexible pavement and repairing materials. In order to extensively explore the process of early cement hydration and the microstructure evolution of PC paste in the presence of cationic AE, various measurements including setting time, hydration heat, conductivity, compressive strength and ultrasonic pulse velocity, Fourier transform infrared spectroscopy (FTIR), chemically bound water, thermogravimetric (TG) and field emission scanning electron microscopy (FESEM) were adopted in the investigation. The experiment results showed that the setting process of PC paste was gradually prolonged with the increase of A/C, implying that the formation of microstructure of PC paste was inhibited by cationic AE, which is in agreement with the hydration heat and conductivity test. The compressive strength and pulse velocity of ultrasonic wave of cement mortar reduced with the incorporation of cationic AE, which thus implied the porosity increases with the addition of A/C, and in turn indicating the generation of microstructure of cement paste was suppressed gradually with the increase of cationic AE, this could also be confirmed by the chemically bound water, FTIR and FESEM results. Finally, the possible retardation mechanism of cement hydration, caused by the cationic AE, was proposed.

The influence of inorganic admixtures on early cement hydration from the point of view of thermodynamics

Calcium salt and other inorganic chemicals have long been used as the accelerators of cement hydration; however, the underlying mechanism remains to be resolved. In this contribution, thermodynamic analysis of cement systems with calcium chloride (0.06 M and 0.12 M), potassium hydroxide (0.28 M and 0.56 M) and hydrochloric acid (0.09 M and 0.18 M) were combined with quantitative analysis of the calorimetric curves of these systems. Calorimetric tests show that calcium chloride and hydrochloric acid would increase hydration rate, whereas lower dosage of potassium hydroxide would decrease hydration rate. Thermodynamic analyses show that in all the systems, the chemical driving force of C3S dissolution keeps increasing whereas that of calcium silicate hydrates (C-S-H) precipitation keeps decreasing, indicating that the dissolution of C3S could be the limiting step of cement hydration. This is further confirmed by the facts that the chemical driving force of tricalcium silicate (C3S) dissolution is positively related to both the intensity of the silicate peak and the occurring time of the silicate peak time, and that the chemical driving force of C3S dissolution is negatively related to the length of induction period. Furthermore, the calcium concentration of pore solution is positively related to the chemical driving force of C3S dissolution, implying that calcium concentration could play a critical role in regulating effect of inorganic admixtures. This work finds the crucial role of C3S dissolution in early cement hydration and also provides new insight into the effect of inorganic chemicals on cement hydration and the mechanism of cement hydration.