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The resistance to chloride penetration of cement-based material with different curing regimes was investigated by solution titration, XRD, LF-NMR and rapid chloride migration test. The results show that the curing regime has influences on the types and structure of the hydration products, which in turn affects their ability to bind chloride ions. The binding capacity of cementitious materials to chloride ions, porosity and chloride ion migration coefficient increased with the increase of water-cement ratio, while steam curing increased the porosity and chloride ion migration coefficient at the same time as it increased the chloride ion binding capacity of the materials. At lower water-cement ratios, the effect of steam curing on the resistance of cementitious materials to chloride ingress is negligible. [ABSTRACT FROM AUTHOR]

Steel slag contains a large amount of calcium silicate, which can react with CO2 to generate CaCO3 and SiO2 colloid, thus steel slag may become a cementitious material with a certain strength. High strength porous steel slag carbonated brick was prepared by adding easily decomposed bicarbonate solid into steel slag as pore-forming agent and then accelerating carbonation. A variety of characterization methods were used to characterize the composition and micro-structure of the samples. The effects of different pore-forming agent dosage and carbonation time on the properties of pore steel slag blocks were discussed. The results show that the addition of ammonia bicarbonate promotes the nucleation and growth of columnar calcite. The strength of steel slag block mixed with 30% pore forming agent can reach 24.8 MPa after 1 day of carbonation, and then the strength development tends to slow down. [ABSTRACT FROM AUTHOR]

The impact toughness and compressive strength of concrete added with calcium carbonate whisker are studied. It is found that calcium carbonate whisker can significantly improve the impact energy consumption at failure of 55 °C steam cured concrete, but has limited impact on 90 °C steam cured concrete. At the same time, SEM, XRD and LF-NMR were used to study the micro morphology, hydration product components and pore structure of the concrete, and the mechanism of the influence of calcium carbonate whisker on the impact toughness and compressive strength of concrete was analyzed. [ABSTRACT FROM AUTHOR]

C-S-H series are synthesized at different temperatures and ages by pozzolanic reaction. The change of particle size distribution, phase composition, morphology and nanostructure of C-S-H with temperatures and ages, and the effects of C-S-H seeds and seeds parameters on the hydration behavior and mechanical properties development of cement were investigated by DLS, XRD, SEM, 29Si NMR, TAM-air isothermal calorimeter and mechanical properties test. The results show that the particle size, crystallinity, basal spacing and Q2/Q1 ratio of C-S-H increases with the increase of synthesis temperature and age. The addition of synthesized C-S-H seeds to cement pastes results in the strong acceleration effect on cement hydration and significant improvement of the early strength of cement paste and mortar. The 1 day-C-S-H seeds synthesized at room temperature can increase the strength of cement paste by about 30 MPa at 12 h. The effect does not show a very regular change with the increase of the temperature and age of seeds synthesis. Considering the effect of C-S-H seeds on the hydration and mechanical properties of cement, and economy and short cycle of seeds synthesis, the C-S-H seeds synthesized at room temperature for 1 day or 55 °C water bath for 12 hours is recommended. [ABSTRACT FROM AUTHOR]

Monocalcium aluminate (CaAl2O4, CA) and quaternary (Q) phase (Ca20Al26Mg3Si3O68) are the two principal hydraulic phases in calcium aluminate cement. Their strength development has been reported. However, little information about the difference of their hydration and hydrates composition is available. For this reason, the hydration process of CA and Q phase was investigated and compared. Results of conductometry indicate that the rate of Q phase hydrates precipitation is much slower than that CA latter. Hydrates identification demonstrates that the most prominent difference between the hydrates for these two compounds is the amorphous AH3 content. The quantity of amorphous AH3 (A=Al2O3, H=H2O) in Q phase hydrates is evidently less than that of CA, as confirmed by FTIR, TG and BSE. Even-distributed amorphous AH3 fills in the crystalline skeleton of calcium aluminate hydrates (C–A–H) enhancing the compactness of CA paste. Hence, CA exhibits a higher 72-day compressive strength than Q phase. [ABSTRACT FROM AUTHOR]

A low-cost and efficient filter medium for Cd(II) removal was prepared by anchoring -SCN functional groups (by 3-thiocyanatopropyltriethoxysilane, TCPS) on ceramsite via the approach of synthesizing a honeycomb calciumaluminum-silicate-hydrate (C-A-S-H) layer as intermediate. The specific surface area of ceramsite was increased enormously by more than 50 times because of the modification of honeycomb layer. Moreover, the abundant Si-OH bonds existing in the structure of CAS-H can serve as active sites for TCPS. The combined effects ensure that the hybrid filter medium (named ceramsite/C-A-S-H/TCPS) demonstrated a high Cd(II) adsorption capacity of 18.27 mg·g1 for particle size of 0.1-0.6 mm, 12.63 mg·g−1 for 0.6-1.25 mm and 8.64 mg g−1 for 1.25-2.35 mm. The Cd(II) adsorption capacity per unit area of ceramsite/C-A-S-H/TCPS (0.1-0.6 mm) is up to 4.07 mg·m−2, which is much higher than that of many nano-adsorbents. In addition, ceramsite/C-AS- H/TCPS could maintain a high removal efficiency (> 85%) in a wide range of pH 3-11 and showed excellent selectivity in the presence of competing ions. Furthermore, Cd(II) could be desorbed from ceramsite/C-A-S-H/TCPS composites with nearly 100%, suggesting the potential application in recycling of heavy metal ions. [ABSTRACT FROM AUTHOR]

Calcium silicate hydrate (C-S-H) with Ca/Si ratio 1.0 was prepared via precipitation in solution and heated at various temperatures to investigate its dehydration behavior. The dehydration, structural collapse and recrystallization characteristics of C-S-H and its microstructural change during heating process were investigated by XRD, SEM, Raman and TG-DSC techniques. C-S-H gradually lost non-evaporable water upon heating, about 50% and 80% non-evaporable water was removed below 200 and 400 °C, respectively, and the rest was removed up to about 1 000 °C. At 400 °C, dehydrated C-S-H exhibited the increasing disordering of calcium/silicon environment and the decreasing symmetrical bending vibration of Si-O-Si of Q2 silicate chains. At 650 °C non-bridging oxygen atoms (Onon) attached to silicon were almost removed, and significant structural change occurred, and at 815 °C C-S-H dehydrated to wollastonite. [ABSTRACT FROM AUTHOR]

We experimentally studied the fine lightweight aggregate with the particle size range of 3.15-4.75 mm used as functional bridge between FRP sheet and concrete substrate. However, problems would appear and how to deal with the interfacial transition zone (ITZ) and make it stronger is the key point for this concept. Considering that silane coupling agent (SCA) can provide a better bond on a silicon-containing material surface, it was introduced as a modifying material to further improve the bond quality of the ITZ between lightweight aggregate and cement paste. Results indicated that the water absorptivity of lightweight aggregate can be controlled by SCA solutions, and the pull-off bond strength, mechanical strength, and microhardness were increased, which was attributed to the optimized microstructure under the condition of an appropriate concentration of SCA. [ABSTRACT FROM AUTHOR]

Composition, morphology, and structure of hydration products in hardened pastes of three kinds of blended cement (cement-silica fume, cement-quartz powder and cement-silica fume-quartz powder) hydrated under different curing regimes (standard curing, 90 °C steam curing, 200 °C and 250 °C autoclave curing) were investigated by X-ray diffraction and field emission scanning electron microscope equipped with EDAX system. Results showed that the main hydration products in three kinds of hardened pastes under standard curing condition are all C-S-H gels, CH, and AFt. Under 90 °C steam curing condition, the main hydration products of cement-silica fume and cement-silica fume-quartz powder are C-S-H gels, whereas those of cement- quartz powder are C-S-H and CH. Under 200 or 250 °C autoclave curing condition, no obvious crystallized CH phase is found in hardened pastes of three kinds of blended cement, and C-S-H gels are transformed into one or more crystalline phases such as tobermorite, jennite, and xonotlite. The chemical composition and morphology of these crystalline phases depend on the composition of mixture and autoclave temperature. [ABSTRACT FROM AUTHOR]

In order to evaluate the exposure risk of lead and cadmium in seafood for coastal residents in the coastline of the South China, representative seafood such as sea fish, crustaceans and molluscs were collected and used as research samples in many sampling points. By determining lead and cadmium content in sample using graphite furnace atomic absorption spectrometry, we carried out a safety evaluation of lead and cadmium contamination of seafood by single factor pollution index method. By calculating lead, cadmium intake of the coastal residents eating seafood, their exposure risk of lead, cadmium was assessed. It was found that, firstly, the content of lead and cadmium in mollusks was both higher than sea fish and crustaceans in the same waters. Secondly, the lead and cadmium pollution in seafood near the mouth of Pearl River was the most serious. Thirdly, lead and cadmium intakes of the coastal population eating seafood were at a basic level of security, but there were certain risks on the males less than 17 years old eating molluscs in Shenzhen Bay. [ABSTRACT FROM AUTHOR]

In order to understand the effect of powders ground from reactive sandstone replacing cement on reducing or suppressing alkali-silica reaction (ASR), and to identify the mechanism of suppressing ASR by this powders, mortar and paste containing reactive sandstone powders of four replacement levels ranging from 10wt% to 40wt% and four specific surfaces areas ranging from 210 m/kg to 860 m/kg were studied. The experimental results showed that incorporation of 40wt% reactive sandstone powders could suppress ASR effectively except for mortar containing reactive sandstone powders with specific surface area of 610 m/kg, which disagreed with the most results reported that the higher reactive powder specific surface area, the smaller ASR expansion. By means of flame photometry, Fourier transform infrared spectroscopy (FT-IR) and thermo gravimetric analysis (TG), the mechanism of reactive sandstone powders on reducing or suppressing ASR was soluble alkalis type of reactive sandstone powders and the competition of liberating and bonding alkali of cement paste containing reactive sandstone powders, when the ability of alkali bonding was greater than the ability of alkali liberation, ASR caused by reactive sandstone was supressed effectively. [ABSTRACT FROM AUTHOR]

Microstructural features including pore size distribution, cell walls and phase compositions of magnesium oxychloride cement foams (MOCF) with various MgO powders and water mixture ratios were studied. Their influences on compressive strength, water absorption and resistance of MOCF were also discussed in detail. The experimental results indicated that moderate and slight excess MgO powders (MgO/MgCl molar ratios from 5.1 to 7) were beneficial to the formation of excellent microstructure of MOCF, but increasing water contents (HO/MgO mass ratios from 0.9 to 1.29) might result in opposite conclusions. The microstructure of MOCF produced with moderate and slight excess MgO powders could enhance the compressive strength, while serious excess MgO powders addition (MgO/MgCl molar ratios = 9) would destroy the cell wall structures, and therefore decrease the strength of the system. Although MOCF produced with excess MgO powders could decrease the water absorption, its softening coefficient was lower than that of the material produced with moderate MgO powders. This might be due to the instability of phase 5, the volume expansion and cracking of cell walls as immersed the sample into water. [ABSTRACT FROM AUTHOR]

The effect of curing regime on degree of Al substituting for Si (Al/Si ratio) in C-S-H gels of hardened Portland cement pastes was investigated by Si magic angel spinning (MAS) nuclear magnetic resonance (NMR) with deconvolution technique. The curing regimes included the constant temperature (20, 40, 60 and 80 °C) and variable temperature (simulated internal temperature of mass concrete with 60 °C peak). The results indicate that constant temperature of 20 °C is beneficial to substitution of Al for Si, and Al/Si ratio changes to be steady after 180 d. The increase of Al/Si ratio at 40 °C is less than that at 20 °C for 28 d. The other three regimes of high temperature increase Al/Si ratio only before 3 d, on the contrary to that from 3 to 28 d. However, the 20 °C curing stage from 28 to 180 d at variable temperature regime, is beneficial to the increase of Al/Si ratio which is still lower than that at constant temperature regime of 20 °C for the same age. A nonlinear relation exists between the Al/Si ratio and temperature variation or mean chain length (MCL) of C-S-H gels, furthermore, the amount of Al which can occupy the bridging tetrahedra sites in C-S-H structure is insufficient in hardened Portland cement pastes. [ABSTRACT FROM AUTHOR]

A C-S-H series with calcium-silicon ratio 0.6-3.0 was synthesized by pozzolanic reaction. Phase composition, nanostructural and morphological characteristics were determined using XRD, XRF, SEM and Si NMR. Most of the samples were phase-pure, poorly crystalline C-S-H. Significant changes in the nanostructure of the C-S-H samples were observed when the calcium-silicon ratio reached values of 0.8, 1.0 and 1.5. At calcium-silicon ratio 0.8 the basal XRD peak began to develop, crosslinking between layers was seen below this ratio but not above, and there was a substantial decrease in mean silica chain length at this ratio. At calcium-silicon ratio 1.0 there was a pronounced microstructural change from granular to reticular and another substantial decrease in mean chain length (indicated by an abrupt increase in the Q peak intensity and decrease in the Q peak intensity). At calcium-silicon ratio 1.5 the basal XRD peak began to diminish again, the mean silica chain length decreased further, and isolated tetrahedra (Q) were observed. [ABSTRACT FROM AUTHOR]

Setting time and strength of sulphoaluminate rapid hardening cement (SAC) incorporated in the presence and absence of silica fume (SF) were determined. Combined with the techniques of isothermal calorimeter, XRD and FSEM, the hydration kinetics of the two systems and the effect mechanism of SF on SAC were investigated. The experimental results showed that SF was proved to be beneficial for SAC system, in terms of setting time and late strength gain. Evidence of accelerator effect of silica fume was found during the first 8 hours of hydration. The formation of AFt was accelerated and the microstructure of the hydration products grew denser with incorporation of SF. SF was proved to play the role of dispersion and setting control at early age and had a greater contribution to later strength due to the increment of crystal nucleation point and the pozzolanic activity. Therefore, SF can be used to not only control the hydration kinetics of SAC, but also develop the late strength and improve the microstructure. [ABSTRACT FROM AUTHOR]

Porous haydite used as waste filter medium was prepared by dreging lake sludge to help solve the treatment problem of sludge and realize its reclamation. Several calcination regimes were considered and their effects on the pore structure and the properties such as the strength, the density, the filtering ability and the phosphate absorption ability of the haydite were investigated. For the mixture of 60% lake sludge and 40% fly ash in this experiment, the calcination regime with a pre-calcination period at about 600 °C, a temperature keeping period at 1 200 °C and a moderate cooling rate are recommended to prepare haydite with reasonable pore structure and good performances for its usage as the waste water filter media. [ABSTRACT FROM AUTHOR]

Purpose: Amide proton transfer (APT) imaging is able to extend the achievable magnetic resonance imaging (MRI) contrast to the protein level. In this study, we demonstrate the feasibility of applying a turbo-spin-echo (TSE)-based, three-dimensional (3D) APT sequence into routine clinical practice for patients with brain tumors. Procedures: Experiments were performed on a Philips 3-Tesla (3-T) MRI scanner using an eight-channel phased-array coil for reception. A fast 3D APT sequence with a TSE acquisition was proposed (saturation power, 2 μT; saturation time, 500 ms; 8 slices). The gradient echo (GRE)-based field-mapping technique or water-saturation-shift-referencing (WASSR) technique was used to acquire B maps to correct for B-induced artifacts in APT images. The test was performed on a box of homogenous protein solution, four healthy volunteers, and eight patients with high-grade gliomas. Results: The experimental data from a homogenous, protein-containing phantom and healthy volunteers show that the sequence produced a uniform contrast across all slices. The average MTR(3.5 ppm) values with GRE B-corrected 3D APT imaging and WASSR-corrected 3D APT imaging were both comparable to the values obtained using the undemanding single-slice acquisition. The average APT image intensity was consistently higher in the tumor core than in the peripheral edema and in the contralateral normal-appearing white matter (both P < 0.001). Conclusion: 3D APT imaging of brain tumors can be performed in about 5 min at 3-T using a routine, commercial eight-channel SENSE coil. [ABSTRACT FROM AUTHOR]

The samples of the C-S-H series were synthesized by hydrothermal reaction of fumed silica, CaO and deionized water at initial C/S ratios between 1.0-1.7. Phase composition and structural and morphology characteristics of C-S-H samples were analyzed by XRD, IR and SEM. The experimental results showed that the d-spacing of (002), (110) and (020) decreased, the d-spacing of (200) increased, and the d-spacing of (310) varied randomly, the polymerization of silica tetrahedra of C-S-H decreased, and morphology of C-S-H samples varied from sheet shapes to long reticular fibers as C/S ratio increased. [ABSTRACT FROM AUTHOR]

The structure characteristics of hydrated calcium silicate synthesized by solution reaction method with the existing of water soluble polymer polyvinyl alcohol (PVA) are investigated. Using NaSO and Ca(NO) as the main raw materials, in the condition of 2%(in weight) addition of PVA and the water to solid ratio of 20, hydrated calcium silicate samples (Ca/Si=1.0 and 1.5) were prepared with 60 °C water bath. IR, BET, XRD and SEM methods were used to study the microstructure of the hydration products. The results showed that the addition of water soluble PVA did not alter obviously the amorphous structure characteristic of hydrated calcium silicate, but it had effects on the polymerization status of Si-O chain and the pore structure. The effects are somewhat obvious in the samples with the Ca/Si of 1.0. [ABSTRACT FROM AUTHOR]

The relationship between autogenous deformation and internal relative humidity (IRH) of high-strength concrete and high-strength expansive concrete were investigated. The experimental results indicate that, there exists a good linear relationship between autogenous shrinkage and IRH of high-strength concrete but a nonlinear relationship between autogenous deformation and IRH of high-strength expansive concrete with expansive agent. The new autogenous deformation curve can be obtained by transforming the autogenous deformation data of high-strength expansive concrete, and there exists linear relationship between the autogenous deformation and IRH. The concept of “critical internal relative humidity” was proposed, which is defined as the value of IRH when autogenous deformation is zero, to effectively reflect the autogenous deformation characteristic of expansive concrete. [ABSTRACT FROM AUTHOR]

To decrease the cement and SF content of RPC by using ultra-fine fly ash (UFFA) and steel slag powder (SS), the effect of these mineral admixtures on compressive strength of RPC were investigated. The experimental results indicate that the utilization of UFFA and SS in RPC is feasible and has prominent mechanical performance. The microstructure analysis (SEM and TG-DTG-DSC) demonstrated that the excellent mechanical properties of RPC containing SS and UFFA were mainly attributed to the sequential hydration filling effect of the compound system. [ABSTRACT FROM AUTHOR]

Due to its low water content, it is difficult for expansive agent to have an effective expansive effect on high strength concrete to compensate its extensive shrinkage and form a certain expansion. To solve this problem, water-releasing material with water storage and releasing characteristics was incorporated into high strength micro-expansive concrete to provide internal curing, and expansive effect of expansive agent was improved. Migration of water from initially saturated water-releasing material to the surrounding hydrating cement paste was investigated. Based on a given efficient diffusion distance of water stored in water-releasing material, the mass and real water-cement ratio of cured cement paste were estimated. At the same time, the effect of internal curing of water-releasing material on the volume deformation of high strength micro-expansive concrete was investigated. [ABSTRACT FROM AUTHOR]

Fly ash (FA) and ground granulated blast-furnace slag (GGBFS) were added to improve the performances of regenerated binding materials (RBM) which refer to dehydrated phases with rebinding ability of waste hardened cement paste. Flowability tests, compressive strength tests, SEM, TG-DSC, and non-evaporable water content tests were employed to study the performances of the combined binding materials and the interactions between RBM, FA, and GGBFS. Results show that adding FA or GGBFS can improve the workability of RBM paste, and GGBFS has positive effects on strength of RBM. Pozzolanic reactions happen between RBM, FA, and GGBFS. And the activation effect of RBM to FA and GGBFS is superior to that of P.O grade-32.5 cement, especially at earlier ages, because of the high reactive f-CaO existing in RBM. On the advantages of the synergetic effects of RBM and pozzolanic admixtures such as FA and GGBFS, new combined binding materials can be prepared by blending them together. [ABSTRACT FROM AUTHOR]

A new way to improve the tunnel fire protection by using flame-retarded porous asphalt pavement containing ATH powders was introduced. Based on the miniature burning test designed and conducted, the burning time and temperature of porous asphalt (PA) and flame-retarded porous asphalt (FRPA) were studied comparing with cement concrete pavement, dense-graded HMA and SMA. Results of burning test and pavement performance test indicate that FRPA is appropriate and suitable as the pavement material of highway tunnel. [ABSTRACT FROM AUTHOR]

Cement and asphalt mortar (CA mortar) is the key component in the structure of Shinkansen slab track and serves as the elastic shock-absorber. A new method was put forward to evaluate the setting process of cement and asphalt emulsion (CAE) in CA mortar. It was noted that the setting process was governed by several factors such as cement types, cement/asphalt emulsion ratios (C/AE ratio). Results also indicated that the setting process of CAE was faster, the higher proportion of cement content was; the early age strength and the separation rate of CA mortar could be improved by using cement of high early age strength and rapid hydration rate, or a blended cement with ordinary Portland cement partially replaced by sulfoaluminate cement, or by increasing C/AE ratio. Nevertheless, the replacement ratio of ordinary Portland cement by sulfoaluminate cement should not exceed 15% and C/AE ratio should be not less than 0.8. [ABSTRACT FROM AUTHOR]

The effects of polyacrylamide (PAM) and polyvinyl alcohol (PVA) on morphology and structure of calcium silicate hydrate with C/S 1.0-1.7 prepared via precipitation in solution were investigated by XRD, FT-IR and TEM techniques. The results show that incorporation of the polymers decreased the order degree, increased the interlayer spacing and disturbed the layered stacking of C-S-H. Interlayer spacing expansion depended on C/S ratios and type of polymer. Interlayer spacing expansion had a minimum at C/S 1.0 and a maximum at C/S 1.3 and 1.5. Interlayer spacing expansion of PAM was bigger than that of PVA with the same C/S. C-S-H added with PVA mainly exhibited foil-like and fibrillar morphology. The fibrils were of variable length from a few tens of nanometers to a few hundreds of nanometers. Fibrils or foils seemed to be longer in the presence of PVA. [ABSTRACT FROM AUTHOR]