Early Age Hydration Research Articles

Improvement of acid resistance of Portland cement pastes using rice husk ash and cement kiln dust as additives

This paper represents a laboratory study on the acid resistance of hardened ordinary Portland cement (OPC) and blended OPC pastes at two different curing temperatures. The blended materials used are rice husk ash (RHA) and cement kiln dust (CKD). The blended cement pastes were prepared using a water/solid (W/S) ratio of 0.3. The effects of immersion in deionized water (pH 7) and sulfuric acid solutions (pH 1, 2 and 3) at two temperatures (20 and 50 °C) on the compressive strength and phase composition of the various hardened blended cement pastes were studied. The results of compressive strength revealed that the increase of curing temperature from 20 to 50 °C resulted in increase the reduction of compressive strength due to acid attack up 2 months, but the resistance to sulfuric acid attack increases after that time due to the formation of crystalline calcium silicate hydrates (CSH) which have higher resistance to acid attack than the amorphous CSH formed at the early ages of hydration. The presence of RHA and CKD improves the resistance to sulfuric acid attack at both curing conditions. From the results of X-ray diffraction analysis and differential scanning calorimetric technique curves, the main hydration products identified are CSH, portlandite, and calcium sulfoaluminate hydrates.

Modelling early age hydration kinetics of alite

The modelling platform μic [1] has been used to investigate the mechanisms occurring during the hydration of alite. It is shown that it is possible to obtain a good simulation of the hydration kinetics through the implementation of two mechanisms: a dissolution mechanism combined with nucleation and growth of products. The dissolution rate is varied according to the ratio β, between the ion activity product and the equilibrium solubility product according the theory published by Juilland et al. [2]. The solution concentrations are computed directly from the amount of alite dissolved taking into account the amount of water present and the amount of products formed, with activities and complex ion formation calculated according to standard methods. Saturation index calculations are implemented to compute the time of precipitation of C–S–H and portlandite (CH) individually. For the main heat evolution peak, the rate controlling mechanism switches to a modified form of boundary nucleation and growth. C–S–H grows in a diffuse manner in which the density of packing of the C–S–H phase increases with hydration [3]. The rate of heat evolution obtained from the simulations is compared with isothermal calorimetry data and good agreement is found.

RETRACTED: The effects of ZrO2 nanoparticles on properties of concrete using ground granulated blast furnace slag as binder

In the present study, flexural strength together with pore structure, thermal behavior, and microstructure of concrete containing ground granulated blast furnace slag (GGBFS) with different amounts of ZrO2 nanoparticles has been investigated. Portland cement was replaced by different amounts of GGBFS, and the properties of concrete specimens were investigated. Although it negatively impacts the physical and mechanical properties of concrete at early ages, utilizing up to 45 wt% GGBFS was found to improve these properties at later ages. ZrO2 nanoparticles with the average particle size of 15 nm were partially added to the concrete with the optimum content of 45 wt% GGBFS, and physical and mechanical properties of the specimens were measured. ZrO2 nanoparticle as a partial replacement of cement up to 3 wt% could accelerate C–S–H gel formation as a result of increased crystalline Ca(OH)2 amount at the early age of hydration and hence, increase flexural strength of the concrete. The more the ZrO2 content of n...

Study on the hydration product of cement in early age using TEM

The morphology, crystallization and elemental composition of cement hydration products in early age including Ca(OH)2, CSH gel, AFt and AFm were investigated by transmission electron microscopy (TEM). Compared with the results from SEM and XRD, the TEM method and its advantage in the investigation of early hydration products were discussed. The results showed that TEM method is more accurate and reliable than SEM in the investigation of early hydration products. The CSH gel was confirmed to be amorphous foil-like shape product with a lot of crumples in early hydration age. Its Ca/Si ratio is 1.3±0.2. The morphology difference of AFt and AFm was clarified. AFt and AFm are both poly-crystal with layered structure, composed of disordered nano crystal. The size of nano crystal is less than 20 nm. The difference of Ca/Si ratio results between SEM and TEM was investigated, and its reason was explained.

Effects of Polycarboxylate Superplasticizers on Hydration and Microstructure of Hardened Cement Paste

Polycarboxylate (PC) superplasticizer was synthesized by radical copolymerization using ammonium persulfate (APS) as initiator at 90 °C for 5 h. The effect of PC on the hydration process and microstructure of hardened cement at different hydration ages (4 h, 1 d and 7 d) was investigated. Hydration of cement paste results show that the nucleation and growth of hydration product of ettringite (Aft) was inhibited by PC at the early hydration ages, and the generation of the hydration products of calcium hydroxide (CH) and calcium carbonate (CaCO3) was promoted at late hydration ages. SEM result indicates that PC can make the structure of hardened cement more homogeneous and more density.

Investigation of the influence of curing temperature and silica fume content on setting and hardening process of the blended cement paste by an improved ultrasonic apparatus

An ultrasonic measurement apparatus (UMA) was developed for in situ continuously monitoring the early age hydration process of cementitious material. Utilizing UMA, the influence of curing temperature and silica fume content on the setting and hardening process of the low water to binder ratio cementitious material were systematically investigated. The experimental results show that setting and hardening process of the silica fume blended cement paste at elevated temperature can be clearly identified into three stages including dormant stage, acceleration stage and deceleration stage. Besides, the increasing of curing temperature and silica fume content greatly accelerate the setting and hardening process of silica fume blended cement paste and increase the ultimate ultrasonic pulse velocity. To aid in comparing with the ultrasonic results, the isothermal calorimetric measurement, Vicat needle test and mechanical properties test were also conducted.

An experimental study on the concrete hydration process using Fabry–Perot fiber optic temperature sensors

This paper describes the contribution of Fabry–Perot (FP) fiber optic temperature sensor to investigate the effects of concrete hydration process. The FP temperature sensor was easily fabricated by controllable chemical etching and adjustable fusion splicing. Detailed optical properties of the sensor were theoretically analyzed and temperature calibration experiments were performed. A sensor with a 90μm cavity length was demonstrated to have a temperature sensitivity of 0.01nm/°C and the linearity coefficient of 0.99. Furthermore, the FP sensor was embedded in the concrete structure for sensing the temperature change during the early age of hydration. During the concrete hydration experiments, the measured peak temperatures of the concrete specimens with different water-to-cement (w/c) ratios of 0.4, 0.5 and 0.6 were 51.42°C, 52.88°C, and 55.08°C, respectively, corresponding to final setting times of 13.52h (w/c=0.4), 14.16h (w/c=0.5) and 15.2h (w/c=0.6) after concrete casting. Temperature profiles will be used for concrete hydration heat study, which will help us to have a better understanding of cement hydration behavior.

Effects of Fe2O3 Nanoparticles on Water Permeability and Strength Assessments of High Strength Self-Compacting Concrete

In this work, compressive, flexural and split tensile strength together with coefficient of water absorption of high performance self-compacting concrete containing different amount of Fe2O3 nanoparticles have been investigated. The strength and the water permeability of the specimens have been improved by adding Fe2O3 nanoparticles in the cement paste up to 4.0 wt%. Fe2O3 nanoparticle as a foreign nucleation site could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH)2 amount especially at the early age of hydration and hence increase the strength of the specimens. In addition, Fe2O3 nanoparticles are able to act as nanofillers and recover the pore structure of the specimens by decreasing harmful pores to improve the water permeability. Several empirical relations have been presented to predict the flexural and the split tensile strength of the specimens by means of the corresponding compressive strength at a certain age of curing. Accelerated peak appearance in conduction calorimetry tests, more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results indicate that Fe2O3 nanoparticles up to 4 wt% could improve the mechanical and the physical properties of the specimens.

NMR research on cement clinker and its structures in early age hydration

Clinker has long been regarded as a critical factor for cement hydration and solidification. α-C2S and β-C2S in 2CaO·SiO2(C2S) phase and C3S Monoclinic 1(C3S M1) and C3S Monoclinic 3 (C3S M3) in 3CaO·SiO2 (C3S) phase were clearly recorded in the 29Si MAS NMR spectra. The content of C3S phase in the clinker deduced from the fine peak analysis coincides with the phase quantification analysis calculated by the Taylor-Bogue method based on XRF, which also accords to the statistical data in industrial production. NMR provides a proof that C3S M1 and β-C2S phases have a prior reaction in the early age hydration of clinker, and demonstrates that aluminum coordination changes from tetracoordinated 4CaO·Al2O3·Fe2O3(C4AF) to hexacoordinated [Ca2Al(OH)6](SO4)0.3·3H2O(Aft) in one day hydration and changes to the 3CaO·Al2O3·CaSO4·nH2O (Afm) in a seven-day hydration.

RETRACTED: The Effects of TiO2 Nanoparticles on Flexural Damage of Self-compacting Concrete

In the present study, flexural strength, thermal properties, and micro- structure of self-compacting concrete with different amount of TiO2 nanoparticles have been investigated. TiO2 nanoparticles with the average particle size of 15 nm were partially added to self-compacting concrete and various behaviors of the speci- mens have been measured. The results indicate that TiO2 nanoparticles are able to improve the flexural strength of self-compacting concrete and recover the negative effects of superplasticizer on flexural strength of the specimens. TiO2 nanoparticle as a partial replacement of cement up to 4 wt% could accelerate C-S-H gel formation as a result of the increased crystalline Ca(OH)2 amount at the early ages of hydration. The increase in the TiO2 nanoparticles' content by more than 4 wt%, reduces the flexural strength because of unsuitable dispersion of nanoparticles in the concrete matrix. Accelerated peak appearance in conduction calorimetry tests, more weight loss in thermogravimetric analysis, and more rapid appearance of peaks related to hydrated products in X-ray diffraction results, also indicate that TiO2 nanoparticles up to 4 wt% could improve the mechanical and physical properties of the specimens. Finally, TiO2 nanoparticles could improve the pore structure of concrete and shift the distributed pores to harmless and few-harm pores.

The effects of CuO nanoparticles on properties of self compacting concrete with GGBFS as binder

In this work, strength assessments and percentage of water absorption of high performance self compacting concrete containing different amounts of ground granulated blast furnace slag and CuO nanoparticles as binder have been investigated. Portland cement was replaced by different amounts of ground granulated blast furnace slag and the properties of concrete specimens were investigated. Although it negatively impacts the physical and mechanical properties of concrete at early age of curing, ground granulated blast furnace slag was found to improve the physical and mechanical properties of concrete up to 45 wt. (%) at later ages. CuO nanoparticles with the average particle size of 15 nm were partially added to concrete with the optimum content of ground granulated blast furnace slag and physical and mechanical properties of the specimens were measured. CuO nanoparticle as a partial replacement of cement up to 3.0 wt. (%) could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH)2 amount at the early age of hydration and hence increase strength and improve the resistance to water permeability of concrete specimens. The increased the CuO nanoparticles' content more than 3.0 wt. (%), causes the reduced the split tensile strength because of the decreased crystalline Ca(OH)2 content required for C-S-H gel formation. Several empirical relationships have been presented to predict flexural and split tensile strength of the specimens by means of the corresponding compressive strength at a certain age of curing. More rapid appearance of the peaks related to hydrated products in X-ray diffraction results, all indicate that CuO nanoparticles could improve mechanical and physical properties of the concrete specimens.

The effects of ZnO2 nanoparticles on properties of concrete using ground granulated blast furnace Slag as binder

In the present study, flexural strength together with pore structure, thermal behavior and microstructure of concrete containing ground granulated blast furnace slag with different amount of ZnO2 nanoparticles has been investigated. Portland cement was replaced by different amounts of ground granulated blast furnace slag and the properties of concrete specimens were investigated. Although it negatively impact the properties of concrete, ground granulated blast furnace slag was found to improve the physical and mechanical properties of concrete up to 45 wt. (%). ZnO2 nanoparticles with the average particle size of 15 nm were added partially to concrete with the optimum content of 45 wt. (%) of ground granulated blast furnace slag and physical and mechanical properties of the specimens was measured. ZnO2 nanoparticle as a partial replacement of cement up to 3 wt. (%) could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH)2 amount at the early age of hydration and hence increase flexural strength of concrete. The increased the ZnO2 nanoparticles' content more than 3 wt. (%), causes the reduced the flexural strength because of the decreased crystalline Ca(OH)2 content required for C-S-H gel formation together with unsuitable dispersion of nanoparticles in the concrete matrix. ZnO2 nanoparticles could improve the pore structure of concrete and shift the distributed pores to harmless and few-harm pores.

Hydration reactions of the system C3A-CaSO4.2H2O (1 : 1 mole ratio) at 30 and 50°C. Part II: Effect of naphthalene formaldehyde sulfonate

Hydration characteristics of tricalcium aluminate and gypsum mixture with a mole ratio of 1 : 1 in the presence and absence of sodium salt of naphthalene formaldehyde sulfonic acid polycondensate (NFS) at 30 and 50°C were investigated. Different ratios of NFS were used, namely 0, 1, and 3% by weight. The water-to-solid ratio used was 10. Hydration was carried out for various time intervals from 0·5 h and up to 90 days. The results of combined water content, X-ray diffraction and scanning electron microscopy indicate that NFS retards the formation of ettringite and accelerates its transformation to monosulfate at early hydration ages. The extent of transformation is inversely proportional to the ratio of NFS.

RETRACTED ARTICLE: Effects of CuO nanoparticles on compressive strength of self-compacting concrete

In the present study, the compressive strength, thermal properties and microstructure of self-compacting concrete with different amounts of CuO nanoparticles have been investigated. CuO nanoparticles with an average particle size of 15 nm were added to self-compacting concrete and various properties of the specimens were measured. The results indicate that CuO nanoparticles are able to improve the compressive strength of self-compacting concrete and reverse the negative effects of superplasticizer on compressive strength of the specimens. CuO nanoparticles as a partial replacement of cement up to 4 wt.% could accelerate C–S–H gel formation as a result of the increased crystalline Ca(OH)2 amount at the early ages of hydration. Increasing CuO nanoparticle content to more than 4 wt.%, causes reduced compressive strength because of unsuitable dispersion of nanoparticles in the concrete matrix. Accelerated peak appearance in conduction calorimetry tests, more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results, all indicate that CuO nanoparticles up to 4 wt.% could improve the mechanical and physical properties of the specimens. Finally, CuO nanoparticles improved the pore structure of concrete and caused shifting of the distributed pores from harmless to low harm.

Modelling early age hydration kinetics of alite

The modelling platform μic [1] has been used to investigate the mechanisms occurring during the hydration of alite. It is shown that it is possible to obtain a very good simulation of the hydration kinetics through the implementation of two mechanisms: a dissolution mechanism combined with nucleation and growth of products. The dissolution rate is varied according to the ratio β, between the ion activity product and the equilibrium solubility product according the theory published by Juilland et al. [2]. The solution concentrations are computed directly from the amount of alite dissolved taking into account the amount of water present and the amount of products formed, with activities and complex ion formation calculated according to standard methods. Saturation index calculations are implemented to compute the time of precipitation of C-S-H and portlandite (CH) individually. Once the pore solution is saturated with respect to portlandite, the rate controlling mechanism switches to a modified form of boundary nucleation and growth. C-S-H grows in a diffuse manner in which the density of packing of the C-S-H phase increases with hydration [3]. The kinetics parameters are calibrated and the same values are used consistently across a range of particle sizes. The rate of heat evolution obtained from the simulations is compared with isothermal calorimetry data and good agreement is found.

The effect of curing temperature on the properties of shrinkage-compensated binder

The effects of curing temperature on the expansive effectiveness, strength, hydration degree, and microstructure of shrinkage-compensated binder were studied. The results showed that under the standard curing temperature (20°C), most crystalline ettringite grows in pores, which makes less contribution to the expansion of paste than gelatinous ettringite blended with C-S-H gel. An elevated curing temperature (40°C) promotes the hydration rate of expansive agent and cement. However, quickly developing strength of paste limits its expansion. The pore structure of hardened paste under moderate curing condition is the densest one among all the pastes cured at different temperatures due to the filling effect of crystalline and gelatinous ettringite. Under a high curing temperature (60°C), the formation of massive stick-like ettringite leads to excessive expansion at early hydration age. Some ettringite decomposes at sustainable high temperature, which decreases the restricted expansion rate of paste at a late age. Appropriate volume expansion is benefit to the improvement of pore structure of hardened paste by reducing large pores.

RETRACTED ARTICLE: TiO2 nanoparticles’ effects on properties of concrete using ground granulated blast furnace slag as binder

In the present study, compressive strength, pore structure, thermal behavior and microstructure characteristics of concrete containing ground granulated blast furnace slag and TiO2 nanoparticles as binder were investigated. Portland cement was replaced by different amounts of ground granulated blast furnace slag and the properties of concrete specimens were investigated. Although it negatively impacts the properties of concrete at early ages, ground granulated blast furnace slag up to 45 wt% was found to improve the physical and mechanical properties of concrete at later ages. TiO2 nanoparticles with the average particle size of 15 nm were partially added to concrete with the optimum content of ground granulated blast furnace slag and physical and mechanical properties of the specimens were measured. TiO2 nanoparticle as a partial replacement of cement up to 3 wt% could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH)2 amount at the early age of hydration and hence increase compressive strength of concrete. The increased TiO2 nanoparticles’ content of more than 3 wt% may cause reduced compressive strength because of the decreased crystalline Ca(OH)2 content required for C-S-H gel formation and unsuitable dispersed nanoparticles in the concrete matrix. TiO2 nanoparticles could improve the pore structure of concrete and shift the distributed pores to harmless and less-harm pores.

Physical and mechanical behavior of high strength self-compacting concrete containing ZrO2 nanoparticles

Abstract In the present study, the compressive strength, thermal properties and microstructure of self compacting concrete with different amounts of ZrO2 nanoparticles have been investigated. ZrO2 nanoparticles with an average particle size of 15 nm were added to self compacting concrete and various properties of the specimens were measured. The results indicate that ZrO2 nanoparticles are able to improve the compressive strength of self compacting concrete and reverse the negative effects of superplasticizer on compressive strength of the specimens. ZrO2 nanoparticles as a partial replacement of cement up to 4 wt.% could accelerate C–S–H gel formation as a result of the increased crystalline Ca(OH)2 amount at the early ages of hydration. Increasing ZrO2 nanoparticle content to more than 4 wt.% causes reduced compressive strength because of unsuitable dispersion of nanoparticles in the concrete matrix. Accelerated peak appearance in conduction calorimetry tests, more weight loss in thermogravimetric analy...

Calorimetric characterization of Portland limestone cement produced by intergrinding

The calorimetric technique provides continuous, direct, and general measurements of the course of coexisting reactions and their interactions during hydration of blended cement at early age. In this article, this technique is used to analyze the influence of compositional and process variables on the early age hydration of Portland limestone cements (PLC) made by intergrinding in a full size-cement plant. Eight cements, the vertices of 23 factorial design, were made with a limestone filler content (LF) of 0 and 24%, a gypsum content (GC) of 2.5, and 5.0%; and a fineness, measured as that fraction retained on a 45 μm sieve (R45), of 5 and 18%, to study their effects on the heat released. In addition, a PLC with a composition nearly to the center point of 23 designs was analyzed. Measurements were performed on cement pastes (w/cm = 0.4) using a semiadiabatic differential calorimeter operating at 20 °C during 48 h. At different time, the heat released was determined and it was modeled using a linear mathematical model including the three variables (LF, R45, CG) and their interactions. The significance of the model, the variables and the interactions was judged using the analysis of variance. Results of model show that heat released is reduced by LF due to physically dilution phenomenon, which is directly proportional to LF content. The R45 exerts its major influence during the development of second peak (12–21 h) but later its effect declines to null contribution. GC retards and attenuates the hydration reactions moderately until 30 h, and then its increase contributes to Qt due to the formation of ettringite and its transformation. The only significant interaction was LF with R45 during the second peak development. Results present good correlation with the isolate measurement of compressive strength at 12, 24, and 48 h.

Research on Set Retarder of High and Super High Strength Alkali -Activated Slag Cement and Concrete

The set of alkali-activated slag cement (AASC) and concrete and the measures for set-retarding were reviewed. Due to the fast set of high and super high strength alkali-activated slag cement and concrete, an inorganic compound set retarder YP-3 was developed. The effect of the retarder on setting time and strength as well as heat evolution of AASC were tested, and the mechanism of the retarder was analysed. Results show that the retarder can regulate the initial set of high strength AASC in the range of 29hrs with little negative effect on its strength development. The retarder could react with silicate ions from liquid to rapidly form a compact film in early age of hydration of AASC, the film covered the surface of slag and obstructed R+ and OH- in contact with slag particle directly. Consequently the set of AAC was delayed.