Hydration Speed Research Articles

Preparation and hydration of low-carbon UHPC with high fraction of activated tuff and recycled fine powders

Due to the high energy consumption and carbon emission of cement, using active supplementary materials in concrete is widely studied. In this paper, waste tuff micropowder and recycled fine powder (RFP) with maximum replaced ratio of 70 % were investigated by alkali activation in ultra-high performance concrete (UHPC), the mechanical properties and hydration process were studied with different dosages and activators. The results show that the strength activity index of tuff and RFP both enhanced after calcium hydroxide activation. The alkali activator accelerated the hydration speed of tuff and RFP, also leaded to a low heat generated. The compressive strength was reduced with the replaced ratio of tuff and RFP, but the flexural strength was improved once tuff added and cured in appropriate temperature. In the cement-tuff/RFP system, calcium hydroxide accelerates cement hydration and activates part of the tuff and RFP to generate C-(A)-S-H to improve the strength of the mortar. Due to the low degree of tuff activation, less hydration products were formed, leaded to an increase in porosity. The RFP was effectively activated by calcium hydroxide, and the generated C-(A)-S-H and CaCO3 effectively refined the pore structure. The activation of RFP consumed limited mixing water, while the excessive CaCO3 generated by activation will cause the loss of UHPC strength.

Reuse of by-product gypsum with solid wastes-derived sulfoaluminate cement modification for the preparation of self-leveling mortar and influence mechanism of H3PO4

Preparing beta-hemihydrate gypsum and then using it for gypsum-based self-leveling mortar (GSLM) in building engineering is one of the promising approaches to consume by-product gypsum such as flue gas desulfurization gypsum and phosphogypsum. In order to overcome the deficiencies of low mechanical strengths and large fluidity loss of beta-hemihydrate gypsum, solid wastes-derived sulfoaluminate cement (WSAC) was used to modify beta-hemihydrate gypsum and prepare GSLM in this work. The effects of various additives on the fluidity and setting characteristics of GSLM prepared using WSAC-modified beta-hemihydrate flue gas desulfurization gypsum was firstly studied, and an optimal formula was obtained. The WSAC-enhanced GSLM had good mechanical performance due to the well-connected structure of the hydration products gypsum and ettringite. However, the hydration speed and degree of GSLM prepared using WSAC-modified beta-hemihydrate phosphogypsum were seriously weakened by phosphorus impurities, which resulted in poor mechanical performance. PO43- would react with Ca2+ and Al3+ dissolved from ye'elimite in WSAC to form CaHPO4·2H2O and AlPO4 precipitates, which seriously inhibited ettringite formation. This negative effect was found mainly acting on the hydration of WSAC and could last until later hydration.

Design and fabrication of high-performance injectable self-setting trimagnesium phosphate

Magnesium phosphate bone cement has become a widely used orthopedic implant due to the advantages of fast-setting and high early strength. However, developing magnesium phosphate cement possessing applicable injectability, high strength, and biocompatibility simultaneously remains a significant challenge. Herein, we propose a strategy to develop high-performance bone cement and establish a trimagnesium phosphate cement (TMPC) system. The TMPC exhibits high early strength, low curing temperature, neutral pH, and excellent injectability, overcoming the critical limitations of recently studied magnesium phosphate cement. By monitoring the hydration pH value and electroconductivity, we demonstrate that the magnesium-to-phosphate ratio could manipulate the components of hydration products and their transformation by adjusting the pH of the system, which will influence the hydration speed. Further, the ratio could regulate the hydration network and the properties of TMPC. Moreover, in vitro studies show that TMPC has outstanding biocompatibility and bone-filling capacity. The facile preparation properties and these advantages of TMPC render it a potential clinical alternative to polymethylmethacrylate and calcium phosphate bone cement. This study will contribute to the rational design of high-performance bone cement.

Strengthening mechanism of granulated blast-furnace slag on the uniaxial compressive strength of modified magnesium slag-based cemented backfilling material

The hydrating active mineral in the modified magnesium slag-based (MMS-based) backfilling material is mainly β-phase dicalcium silicate characterized with slow speed of hydration and low early strength. This disadvantage restricts the application of modified magnesium slag (MMS) as cementitious material in backfilling mining to some extent. In this work, the strengthening mechanism of granulated blast-furnace slag (GBFS) on the uniaxial compressive strength (UCS) of MMS-based cemented backfilling material has been investigated systematically. The hydration heat tests reveal that the duration of induction and acceleration periods are gradually shortened and the appearance time of the second exothermic peaks are obviously advanced as the proportion of GBFS increases. The total normalized hydration heat releases of MMS-based pastes containing 0, 1%, 2%, 3% and 4% (solid-mass proportion) GBFS at 120 h are 15.76, 16.02, 18.40, 22.31, and 25.54 J/g, respectively. Compared with the blank control group, the hydration heat release of MMS-based paste at 120 h increased by 62% with addition of 4% (solid-mass proportion) GBFS. In addition, the TG-DTG tests shown that the final mass-losses of MMS-based cemented backfilling materials tend to increase with the increase of the amount of GBFS. The 3- and 7-days UCSs of MMS-based backfilling mortars tend to increase dramatically with the increase of proportion of GBFS. A small amount of GBFS (1 wt%) can significantly improve the 28- and 56-days UCSs of the MMS-based mortars. Compared with the blank control group, the UCSs of MMS-based mortars cured 3, 7, 28, and 56 days increased by 74.2%, 94.6%, 38.0%, and 24.1% respectively with addition of 5% (solid-mass proportion) GBFS. The SEM, XRD, FTIR, and TG-DTG tests show that the MMS-based mortars containing GBFS generated more hydration products, yielded more compact microstructures, and consumed CH more quickly compared with that of blank control group. Compared with fly ash (FA), GBFS dissolves faster in alkaline media (leaching reactive Al and Si early), and releases much more hydration heat and Ca2+ ions during the process of pozzolanic reaction. The above three factors strengthen the UCS of MMS-based mortar. The results of this study can provide theoretical guidance for the raw material ratio design and field application of MMS-based cemented backfilling paste.

Effect of Vigileo/FloTrac System-Guided Aggressive Hydration in Acute Myocardial Infarction Patients to Prevent Contrast-Induced Nephropathy After Urgent Percutaneous Coronary Intervention

Tailored hydration strategies appear to provide an effective solution for preventing contrast-induced nephropathy (CIN) after percutaneous coronary intervention (PCI). The Vigileo/FloTrac system could predict the patients' fluid responsiveness and tolerance to hydration. This prospective multicenter, randomized controlled, open-label study evaluated the efficacy of aggressive hydration guided by the Vigileo/FloTrac system for CIN prevention in patients with acute myocardial infarction (AMI). This trial enrolled patients with AMI undergoing urgent PCI, and these patients were randomized (1:1) to receive either aggressive hydration guided by Vigileo/FloTrac system (intervention group) or general hydration (control group). Patients with AMI in the intervention group received a loading dose of saline, and the hydration speed was adjusted according to the change of Vigileo/FloTrac index. The primary end point is CIN, which was defined as a >25% or >0.5mg/100ml increase in serum creatinine compared with baseline during the first 72hours after urgent PCI. This trial was registered in ClinicalTrials.gov (NCT04382313). A total of 344 patients with AMI were enrolled and randomized in our trial, and the baseline characteristics, including risk factors of CIN, of the Vigileo/FloTrac-guided hydration group (n=173) and control group (n=171) were well balanced (all p >0.05). The total hydration volume in Vigileo/FloTrac-guided hydration group was significantly much more than control group (1,910 ± 600 vs 440 ± 90ml, p <0.001). The incidence of CIN in the Vigileo/FloTrac-guided hydration group was significantly decreased than that in the control group (12.1% [21/173] vs 22.2% [38/171], p=0.013). There was not significantly different in the incidence of acute heart failure after PCI (9.2% [16/173] vs 7.6% [13/171], p=0.583). The incidence of main adverse cardiovascular events in the Vigileo/FloTrac-guided hydration group was lower than that in the control group but without statistically difference (30 events [17.3%] vs 38 events [22.2%], p=0.256). In conclusion, Vigileo/FloTrac system-guided aggressive hydration could effectivelydecrease the risk of CIN for patients with AMI undergoing urgent PCI and avoid attack of acute heart failure at the same time.

The study of nanosilica in cement base materials

The effect of nanoparticles of nanosilica on the characteristics of the systems of cement-sand-water is studied. In the studies, 50–110 nm nanoparticles obtained through the separation of nanosilica from the soluble glass using the method of sol-gel were applied. The characteristics of solid samples were measured after their hardening during 3-28 days. The effect of nanoadditive on the density, speed of accumulation of final durability of cement samples in squeezing was defined. Obtained results on the increase of durability in squeezing of solid cement samples should be explained with the effect of nanostructuring achieved with adding nanoparticles of silica. These particles are characterized with high specific surface and its high physical-chemical activity. It is shown that due to the effect of surface of silica nanoparticles, hydration speed of cement rises and direct formation of ordered permolecular structures of hydrates of calcium silicate structuring the cement matrix and improving its hardness occurs. The results may be applied in construction technologies for the structuring of cement materials and improving their characteristics as well: durability, density, water permeability, cold resistance.

Calculation and Analysis of Nonlinear Algorithm for Stability of Nanosilica Powder Soft Soil Pile Foundation.

In order to reasonably evaluate the stability of the embankment supported by the rigid pile composite foundation, a nonlinear algorithm calculation and analysis method for the stability of the nanosilica powder soft soil pile foundation is proposed. First, the soft soil foundation reinforced by the composite structure of “piles (prestressed pipe piles, (cement fly-ash gravel, CFG) piles)—pile caps—geotextile pads” is analyzed through the soft soil embankment test section of the Wenfu high-speed railway. Second, the compressive modulus under one-dimensional confining compression is calculated using the layered summation method. Finally, the deep lateral deformation of the pile foundation soil is measured by an inclinometer to evaluate the actual displacement of the pile foundation soil. In the standard method, the empirical coefficient 1.1–1.7 is multiplied on the basis of the calculation result of this method to correct the calculation error. Combined with the test results, it is shown that nanosilica powder can give full play to its excellent characteristics: promoting hydration speed and hydration degree through the reaction of pozzolan refining and consuming Ca(OH)2 crystals produced by cement hydration. Soft soils and modified soft soils: a certain amount of nanosilica powder can significantly improve the strength of soft soil at different ages.

Early-age mechanical properties and hydration degrees of magnesium phosphate cement paste in freezing winter of cold regions

Magnesium phosphate cement (MPC) paste is a good patching material for concrete repair works. This study focused on early-age mechanical properties and hydration degrees of MPC paste in freezing winter of two types of cold regions, which are highland regions and high-latitude regions. MPC pastes with different mix proportions under different curing modes were experienced a series of experiments, including fluidity and setting time, compressive strength, pore structure characterization, thermogravimetric analysis, X-ray diffraction and electron microscopic scanning. Results showed that for winter applications, MPC pastes in simulated highland temperature conditions performed better than those in true high-latitude temperature conditions, illustrated by pore structure analyses and hydration products analyses. The best M/P ratios for highland applications and high-latitude applications were respectively 4 and 5, which respectively delivered 24 h strengths at about 50 MPa and 25 MPa. Even in severe cold winter, the setting of MPC paste depended on the hydration speed instead of the frozen action. Mixing water temperature was good for early-age hydration of MPC paste which cured for six hours in natural cold environment, however, the effect vanished at 24 h. Both the amounts of struvite and unhydrated phosphate, which could be quantitatively assessed by TG-DSC tests or qualitatively assessed by XRD test, were good indicators of the hydration degree of MPC paste in cold weather. These results provided valuable suggestions for winter applications of MPC paste in different types of cold regions.

Water absorption and storage tolerance of soybean seeds with contrasting seed coat characteristics

Seed coat characteristics may be related to seed quality and longevity, attracting the interest of breeding programs. This study aimed to evaluate the relationship between the water absorption parameters and storage tolerance of soybean seeds with contrasting seed coat characteristics. For this purpose, seeds of five soybean cultivars with different seed coat colors and lignin contents were used. Before storage, the seed coat lignin content, moisture content, water absorption rate in 11 hydration periods (1, 2, 3, 4, 5, 6, 7, 8, 24, 32, and 48 hours), hydration speed index, germination, viability, and seed vigor were determined. After six months of storage in a dry and cold chamber (at 11ºC and 54% relative humidity [RH]) and uncontrolled environment (at 25ºC and 71% RH), the seeds were evaluated for germination, viability, and vigor to quantify changes in their physiological quality during storage and relate them to the seeds water absorption parameters for the different cultivars. The seed coat lignin content is negatively correlated with the seeds water absorption parameters. Soybean cultivars have different storage tolerance levels. Seeds that absorb larger amounts of water have lower tolerance to deterioration related to temperature and relative humidity fluctuations that occur in storage under uncontrolled conditions, negatively affecting the physiological potential of seeds.

One-part alkali activated slag using Ca(OH)2 and Na2CO3 instead of NaOH as activator: more excellent compressive strength and microstructure

In this paper, sodium carbonate and calcium hydroxide instead of sodium hydroxide used as composite activators, and slag are applied to prepare one-part alkali-activated slag. Furthermore, the properties of the slag activated by sodium hydroxide are compared. The compressive strength, XRD, TGA, MIP, and SEM analysis of the two systems are performed. The results show that the one-part alkali-activated slag prepared from sodium carbonate and calcium hydroxide has a superior compressive strength against the slag activated by sodium hydroxide. It is also found that the hydration speed of the sodium hydroxide activated slag is faster, and thus the higher compressive strength of the one-part alkali-activated slag is not caused by the hydration speed. The hydration of one-part alkali-activated slag produces a certain amount of calcium carbonate, resulting in a lower porosity in comparison with the slag activated by sodium hydroxide, which may be the reason for the better compressive strength of one-part alkali-activated slag.

Early hydration behavior of novel amphoteric polymer in cement paste

The development of the early strength of the concrete mainly depends on the early hydration process of the cement, and there are many factors influencing the early hydration process of the cement. It is of great significance to study the mechanism of the polymer on the cement hydration for the development of the product. The amphoteric polymer was synthesized by (2-propenyloxyethyl) trimethyl ammonium chloride, acrylic acid and isopentene polyoxyethylene ether with different molar ratio. The chemical structure of polymer was characterized by GPC, and the performance of cement with polymers was observed by isothermal calorimetry and compressive strength of mortar. The results showed that the new amphoteric polymer has a strong promoting effect on the early hydration of cement. With the increase of the amount of (2-propenyloxyethyl) trimethyl ammonium chloride, the hydration speed is faster, but the addition of amphoteric polymer results in the decrease of fluidity of cement paste, so it is necessary to control its amount reasonably.

Two aquaporins, SIP1;1 and PIP1;2, mediate water transport for pollen hydration in the Arabidopsis pistil.

Pollination is the crucial initial step that brings together the male and female gametophytes, and occurs at the surface of the stigmatic papilla cell in Arabidopsis thaliana. After pollen recognition, pollen hydration is initiated as a second critical step to activate desiccated mature pollen grains for germination, and thus water transport from pistil to pollen is essential for this process. In this study, we report a novel aquaporin-mediated water transport process in the papilla cell as a control mechanism for pollen hydration. Coupled with a time-series imaging analysis of pollination and a reverse genetic analysis using T-DNA insertion Arabidopsis mutants, we found that two aquaporins, the ER-bound SIP1;1 and the plasma membrane-bound PIP1;2, are key players in water transport from papilla cell to pollen during pollination. In wild type plant, hydration speed reached its maximal value within 5 min after pollination, remained high until 10-15 min. In contrast, sip1;1 and pip1;2 mutants showed no rapid increase of hydration speed, but instead a moderate increase during ∼25 min after pollination. Pollen of sip1;1 and pip1;2 mutants had normal viability without any functional defects for pollination, indicating that decelerated pollen hydration is due to a functional defect on the female side in sip1;1 and pip1;2 mutants. In addition, sip1;1 pip1;2 double knockout mutant showed a similar impairment of pollen hydration to individual single mutants, suggesting that their coordinated regulation is critical for proper water transport, in terms of speed and amount, in the pistil to accomplish successful pollen hydration.

Durable poly(N-isopropylacrylamide) grafted PDMS micropillared surfaces for temperature-modulated wetting

Surface grafting of polymer brushes has become an area of significant research to deliver desired material properties such as smart wetting. In this research the grafting of Poly(N-isopropylacrylamide)(PNIPAAm) by benzophenone-initiated UV polymerization on micro-pillared surfaces was performed. By increasing polymerization time PNIPAAm first coats the top of the mushroom pillars then bridges the gap between pillars rather than penetrating the inter-pillar spaces due to the intrinsic features of Poly(dimethylsiloxane) (PDMS) pillars. This enables controlled grafting via control of polymerization time. Above the lower critical solution temperature (LCST), the grafted PNIPAAm brushes are immiscible with water and the surfaces displayed a strongly hydrophobic state with a large contact angle of 120°. Below the LCST, the grafted PDMS micropillars surface swells and absorbs water significantly faster than flat grafted surfaces, displaying a hydrophilic state with a small contact angle 33°. Interestingly, grafting on micropillars as opposed to flat surfaces enhanced the magnitude of the contact angle change across PNIPAAm’s hydrophobicity-hydrophilicity switch and enhances the speed of graft hydration. The grafted surface was further found to be durable under strong water jetting. Thus, a significant synergetic effect of the grafted PNIPAAm and micropillars delivered a durable temperature-modulated smart wetting property with a transition from the hydrophobic to hydrophilic state.

EFFECT OF COMPLEX ADDITIVE ON EXOTHERMIC KINETICS AND HYDRATION STAGES OF CEMENT SYSTEMS

The influence of complex additives on the kinetics of cement exothermia and the stage of cement hydration at hardening of heavy concrete in industrial conditions has been studied. It is established that in heavy concrete B35 with the use of cement CEM I 42.5 N SS with complex admixture maximum temperature of hydration - 79.0 ° C reaches 26 hours 30 minutes after pouring and preservation of maximum temperature within 78.0-79.0 ° C continues for 9 hours. Complex additives significantly increase the degree of hydration of cement. At the same time, the initial hardening time is 4-4.5 % and 28 day hardening age is up to 15 %. It is established that the introduction of complex additive in the cement composition of CEM I 42.5 N SS promotes the formation of smaller and mostly oriented secondary crystals of Portlandite. The considered complex additives consisting of the active mineral additive (wastes of enrichment of polymetallic ores), nanofiller (microsilica) and chemical additives (master air 200 and master rheobuid 1000) changing speed of hydration and time of achievement of the maximum temperature index, define the periods of hydrate formation.

Controlled morphologies and hydration process of hydratable alumina by using citric acid

Hydration mechanisms of hydratable alumina (HA) in citric acid at different pH are investigated in this study, aiming to improve rapid hydration process and massive hydration heat. By adding citric acid to adjust solution pHs to 2, 3, and 4, the crystal phase, morphologies, and microstructure of the HA hydrates are characterized by X-ray powder diffraction (XRD), differential scanning calorimetry (TG-DSC), and transmission electron microscopy (TEM), respectively. The results show that HA exhibits different hydration behaviors in different concentrations of acidic solutions. With decreasing pH of citric acid, the crystallinity of HA decreases whereas the dehydration process slows down. Excessive citric acid could displace hydroxyl which generates from pseudoboehmite gel. Meanwhile, the excess citrate ion can be absorbed on the surface of HA by forming numerous micelles, then compound to inhibit further hydration. Proper addition of citric acid helps to delay the hydration of HA and achieve better balance between bonding performance and hydration speed.

Experiment and simulation on the integrity of cement ring interface in deep water shallow formation

The integrity of cement ring interface is critical for the safe production of crude oil and nature gas and the protection of marine environment in deep water shallow formation. Due to the slow hydration speed of the cement under low temperature and the low compaction of the weakly consolidated formation, the casing-cement-formation interfaces are prone to generate micro-annulus. In this paper, a device for testing the interface radial bond strength was designed. The test results showed that the cement-casing interface radial bond strength gradually increased with the increase of curing temperature, and the cement-formation interface radial bond strength increased with the decrease of water content in the formation. Based on ABAQUS finite element software, the tensile stress on the cement-casing interface during the reduction of casing internal pressure, and the tensile stress on the cement-formation interface during the hardening and shrinking process of cement were studied. When the casing internal pressure reduced, the hardened cement with high elastic modulus generated greater tensile stress on the cement-casing interface. The casing internal pressure reduction should not exceed 2.49, 2.75 and 5.41 MPa at the formation temperature of 4, 7 and 10 °C, respectively. In addition, the cement slurry used in this paper can be well bonded with the weakly consolidated formation in deep water shallow formation. This paper is of great significance to study the failure mechanism of cement ring interface integrity in deep water shallow formation, and has guidance for proposing corresponding rationalization suggestions and measures.

Experimental study on the damage of organic-rich shale during water-shale interaction

Water-shale interaction remains an unsolved problem because of the complexity involved in the physical processes and the heterogeneity in the chemical composition and pore structure of rocks. By considering the basic physical properties of Longmaxi shale and performing a series of physical experiments representing the water-shale interaction, the relationship between the mineral composition and water-shale interaction, which is the process responsible for causing structural damage when water and shale interact, is analysed. The ion exchange of clay minerals occurs when shale makes contact with water and different kinds of cations experience different degrees of overflow in water-shale interaction. The charge of clay mineral changes during water-shale interaction, resulting in a change of the gravitational and repulsive forces between the particles. This leads to the passivation of the contour edges of clay minerals and changes in the mechanical properties. In a relatively short time, illite can produce a large hydration stress with a small expansion value, but the hydration speed of Na-montmorillonite (Na-MMT) is relatively slow. Uneven stress caused by the hydration of different clay minerals being soaked in different aqueous solutions can cause local stress concentration, further promote the expansion and increase of original micro-cracks in shale, and then appear as disordered macro-cracks. The macroscopic cracks also provide a channel for the continuous entry of working fluid. More water molecules enter the shale faster and make contact with clay particles, weakening the interaction and cementation between particles. Macroscopically, they are manifested as a decrease in the rock cohesion, internal friction angle, and compressive strength as well as a failure of the structural integrity. Different inorganic salt solutions have different inhibitory effects on reducing the hydration degrees of illite and Na-MMT. Therefore, the water-shale interaction of organic-rich shale is a process in which the microscopic damage of water to rock gradually evolves into macroscopic damage, and results in the local continuity loss of rock on the basis of surface hydration, ion hydration, and osmotic hydration of clay minerals. The higher the clay mineral content, the more likely that hydration will occur, resulting in more serious shale structure damage and a shorter time for damage to occur.

High altitude headache among tourists visiting the high altitude city of La Paz Bolivia at 3.600 meters above sea level

Exposure to high altitude causes physiological changes of acclimatization. Factors such as: genetics, age, speed of ascent, habits and hydration among others intervene. The direct ascent to high altitude is a main factor for the development of high altitude headache. An observational, cross-sectional, descriptive study conducted in the city of La Paz at 3600 meters over sea level, the Lake Louise scoring system was applied to 287 tourists of European origin between the ages of 20 and 35 who arrived for the first time directly to the city by air without stops. 49.2% did not present headache (50% men, 48.6% women), 24.9% mild headache (26% men, 23.4% women), 14.6% moderate headache (12%) males, 16.8% women), 11.4% severe headache (12% males, 11.2% females). 32.4% did not present fatigue (29.5% men, 34.6% women), 44.3% mild fatigue (47.4% men, 42.1% women), 16.8% moderate fatigue (16, 7% males, 16.8% women), 6.5% severe fatigue. 72.4% sleep well as usual (67.9% male, 75.7% female), 17.3% do not sleep as well as usual (20.5% male, 15% female), 7% wake up many times , little sleep (9% males, 5.6% females), 3.2% cannot sleep (2.6% males, 3.7% females) The direct ascent of young tourists from sea level to 3600 meters above sea level did not have a significant impact on the development of height headache and other signs of altitude sickness

Effects of fly ash microspheres on sulfate erosion resistance and chlorion penetration resistance in concrete

Fly ash microsphere (FAM) is a superfine fly ash product consisting of perfectly spherical and smooth particles. In this study, FAM was added to concrete for use in saline soil areas. The replacement levels of cement by FAM were 10% and 20% with a water-to-binder (w/b) ratio of 0.42. The hydration heat, thermogravimetric (TG) analysis, rheological performance, and the flowability of pure cement (CF0) and FAM-doped cement (CF10 and CF20) were investigated. The second exothermic peak occurred earlier and was higher in the FAM-doped cement than the CF0. The results showed that the nucleation effect of the FAM accelerated the early hydration speed of the cement. The TG results indicated that the Ca(OH)2 consumption was higher at 28 days due the addition of the FAM, which improved the interfacial transition zone and blocked the connected porosity of the hardened cement paste. The ball-bearing effect of the FAM particles in the paste reduced the internal friction between the grains, thereby significantly improving the rheology and the flowability of the cement paste. In addition, the filler effect of the FAM particles significantly improved the pore structure, which increased the compressive strength and chlorion penetration of the concrete. It was also found that the FAM increased the workability while improving the resistance of the concrete to sulfate attack when exposed to multiple drying–wetting cycles.

The influence of the hydration procedure of MgO expansive agent on the expansive behavior of shrinkage-compensating mortar

The objective of this paper is to evaluate the influence of the hydration process of MgO expansive agent in binder on the expansion of shrinkage-compensating mortar. The variation of MgO and Mg(OH)2 content in binder at certain curing ages was examined quantitatively through X-ray diffraction (XRD) Rietveld analysis. Expansive behavior of shrinkage-compensating mortars containing MgO expansive agent was also investigated as a comparison with the hydration process. Results indicated that the hydration speed of MgO is determined by its reactivity, highly reactive MgO results to a fast hydration and expansion speed. The curing condition (sealed or saturated) hardly influences the hydration speed of MgO, but largely influences the expansion rate of mortars. The expansion effect due to MgO hydration lags behind its reaction in the binder paste. Sufficient pore water contributes to the recrystallization of Mg(OH)2, which thus causes high crystal growth pressure and promotes the expansion of mortars.