This article focuses on discussing the development situation of the Chinese cement industry at present, in recent years and as a foreseeable trend over the next few decades. In particular, special emphasis is placed on the current situation regarding imports and exports, overseas investment, the paring down of excessive industrial capacity, and the future prospects of the cement industry in China.
The influence of sodium sulfate (SS) addition on hydration and microstructure development of the cement high volume fly ash (CHVFA) system under steam curing is investigated in this paper. The compressive strength of CHVFA mortars was tested with different SS dosages. Results show that the addition of SS increases the strength obviously when its content is less than 2 %, and that further increase in SS content is not conducive to the development of strength. The mechanism of the positive effect of SS is analyzed by X-ray diffraction (XRD), differential scanning calorimetry-thermogravimetry (DSC-TG), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR). The results reveal that SS incorporation accelerates the hydration of cement and fly ash, decreases the porosity and the content of calcium hydroxide (CH) and increases the polymerization degree of C-S-H, thus enhancing the compressive strength of mortars.
Pulverized coal combustion was investigated for bituminous coal and anthracite at different temperatures (973K and 1173K) in a horizontal fixed-bed reactor test system using computational fluid dynamics (CFD) software. The high temperature sufficed to promote NOx formation. For coals of identical mass, much more NOx formed during anthracite combustion than was the case for bituminous coal, but the maximum NOx concentration for bituminous-coal combustion was higher. Two experimental results are mutually complementary, providing important theoretical guidance for exploring the gaseous products of pulverized-coal combustion. Choosing anthracite as fuel and locating the coal inlets in the low-temperature zone could reduce the level of NOx emissions in the cement industry.
The aim of this work is to investigate the effect of 0.5?% addition of cupric nitrate on the setting time, heat flow curves, hydration and compressive strength of remaining slag (RS) from a Ti-Si-Fe making process based on titanium-bearing BF slag, the chemical and mineral compositions of which are similar to those of calcium aluminate cement. Cupric nitrate can cause a delay in the initial setting and final setting time of remaining slag. Maximum heat liberation occurs later and less pronounced when cupric nitrate is added. Hydration was identified by means of XRD,TG-DSC and SEM. All results showed the hydration products at 1d of CAH(10) to have decreased significantly in RS laced with Cu, while the C(2)AH(8) content increased at first, later converting to stable C(3)AH(6) with continuing hydration.
The influence of nano-TiO2 (NT) on the mechanical properties and hydration characteristics of a cement high-volume fly ash (CHVFA) system were studied in this paper. The compressive strength of CHVFA mortars was tested with different FA and NT contents. Results show that the addition of NT increases the strength significantly, while the degree of enhancement wanes with increasing length of the curing. The mechanism of NT on properties of the CHVFA system was analyzed by X-ray diffraction (XRD), differential scanning calorimetry-thermogravimetry (DSC-TG), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR). The results reveal that the addition of NT accelerates the hydration of cement and fly ash significantly, but the promotion effect is delayed along with the curing age, thus lessening the facilitating role of NT on the compressive strength of CHVFA mortars.
The effect of 0.5 wt.% lead nitrate on the early hydration of high alumina cement (HAC) that contains spinel was examined by isothermal calorimetry, XRD, TG-DSC and SEM. Lead nitrate affects the hydration and both the initial setting time and final setting time were extended. Lead nitrate also reduced and delayed the maximum rate peak of hydration of HAC. The pH value of HAC paste was significantly lower in the early stages when compared with the addition of lead nitrate. It was found that an NO3-hydrate phase (Ca4Al2(NO3)(2)(OH)(12) center dot 4H(2)O, NO3-AFm) was formed at 6 h. Although the characteristic value of the hydrated calcium aluminate (CAH(10)) was decreased, the characteristic values of the hydrated dicalcium aluminate (C(2)AH(8)) and tricalcium aluminate (C(3)AH(6)) were increased significantly. That means that lead nitrate promotes the early generation of NO3-AFm in HAC, which will delay early hydration. However, after 18 h lead nitrate promotes C(2)AH(8) or transformation of the metastable needle-shaped or hexagonal CAH(10) into stable cubic C(3)AH(6).
In the search for an effective way of increasing the early strength of cement systems containing a high volume of fly ash (CHVFA), nano-silica (NS) was used in the CHVFA systems with two curing modes: standard curing (20 +/- 2 degrees C, RH >= 95 %) for 3 days and steam curing (65 +/- 2 degrees C, RH >= 95 %) for 12 h and then standard curing for 60 h. The effect of NS and curing temperature on the hydration of cement and fly ash and on the pore structure of the paste were studied in the search for the underlying mechanism.
This study is intended to assess the ability to counter chloride diffusion of concrete applied with inorganic coating modified with different additives including fly ash (FA), silica fume (SF) and nano-SiO2 (NS). Experimental results reveal that the resistance against penetration of chloride is improved in the concrete specimens coated with special mortar coating compared to the non-coated specimen. Especially, concretes with NS modified mortar coating exhibit the most remarkable performance. Then the influence mechanisms of mortar coating mixed with different additives on the anti-chloride ion permeability of concrete are investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP). The results of the analyses indicate that the micro-aggregate filling effect of FA increased the density of the mortars, and thus reduced the chloride diffusion coefficient of the concrete. Three effects of SF and NS, including the heterogeneous nucleus effect, the high pozzolanic activity and the micro-aggregate filling effect, together increased the resistance to the chloride ion permeability of cement-based materials.
The influence of nano-SiO2 (NS) and basalt fiber (BF) modified cementitious coatings on chloride permeability in concrete and the influence mechanism explored by differential scanning calorimetry thermogravimetry (DSC-TG), X-ray diffraction (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) was studied. Results show that the chloride penetration resistance was significantly improved in the concrete applied with special mortar coating as compared to the non coated variety, especially in concrete applied with 5 % NS and 0.5 % BF in a 6 mm modified mortar coating. Moreover, the mechanism analysis reveals that, all together, the heterogeneous nucleus effect, the high pozzolanic activity and micro-aggregate filling effect of NS, the inhibiting effect of BF on connected cracks and pores, and their grading advantage and synergy, improved the ability of concrete to counter chloride diffusion.
The influence of nano-TiO2 (NT) on impermeability to chloride ions of mortars was studied by the rapid chloride migration (RCM) method, and the improvement mechanism was analyzed by X-ray diffraction (XRD), differential scanning calorimetry-thermogravimetry (DSC-TG), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). Results show that the addition of NT helps strengthen the chloride resistance of mortars. Dosages of 1 %, 2 % and 3 % reduce the chloride diffusion coefficient by 6.6 %, 19.4 % and 31.1 %, respectively. It is concluded from mechanism analysis that the micro-aggregate filling effect and the heterogeneous nucleation effect promoting the generation of hydration products of NT, together affect the pore structure and compactness of mortars, further improving their ability to counter chloride diffusion.
The influence of nano-TiO2 (NT) on the rheological parameters, fluidity, and setting time of a fly ash (FA)-cement system is studied and the influence mechanisms are investigated by hydration heat, X-ray diffraction (XRD) and differential scanning calorimetry-thermogravimetry (DSC-TG). Results show that the addition of NT with high special surface area increases the plastic viscosity and yield stress, decreases the fluidity and shortens the setting time of cement paste, and that the extent of variation is related to the content of FA. In addition, incorporating NT, which has a heterogeneous nucleation effect, promotes the hydration and hardening of cement and accelerates the formation and precipitation of calcium hydroxide (CH) at an early stage. FA substituting the same quantity of cement is unfavorable to the generation of CH. However, the perfectly spherical structure and micro-aggregate filling effect of FA improve the rheological behavior of fresh paste and restrain the setting and hardening of cement.