建筑工程中大体积混凝土施工技术分析

当前,科学技术的发展促使大体积混凝土施工技术不断进步,但是在实际的施工过程中仍然存在一定的问题,对大体积混凝土结构的质量产生一定的影响,因此在具体施工中,施工单位应重视技术优化,提升施工质量。本文深入分析了大体积混凝土施工材料用量大、程序复杂和裂分问题严重等特点,并分析了裂缝问题产生的原因以及解决措施,以期优化施工技术,促进我国建筑行业进步。

Recovery of titanium from undissolved residue(tionite) in titanium oxide industry via NaOH hydrothermal conversion and H_2SO_4 leaching

To recover titanium from tionite, a new process consisting of NaOH hydrothermal conversion, water washing, and H2SO4 leaching for TiO2 preparation was developed. The experimental results show that under the optimum hydrothermal conversion conditions, i.e., 50% NaOH （mass fraction） solution, NaOH/tionite mass ratio of 4：1, reaction temperature of 240 ℃reaction time of 1 h and oxygen partial pressure of 0.25 MPa, the titanium was mainly converted into Na2TiO3, and the conversion was 97.2%. The unwanted product Na2TiSiO5 remained stable in water washing, and its formation was prevented by improving NaOH concentration. In water washing process, about 97.6% of Na＋ could be recycled by washing the hydrothermal product. The NaOH solutions could be reused after concentration. 96.7% of titanium in the washed product was easily leached in H2SO4 solution at low temperatures, forming titanyl sulfate solution to further prepare TiO2.

Thermal Analysis of Composite Cements

The hydration of cement compounds gives hydrated compounds, which allow linking together, the different particles and aggregate of cement, and gives the concrete the required qualities. The dynamics of hydration reactions will depend on many factors, such as the fineness of cement, the ratio w/c during hydration, temperature, mixing technique, and the presence of additives in blended cement, as pozzolan, tuff and slag from blast furnaces. We studied the thermal and kinetic reactions of Portland cement hydration, and its variants with different additions using a differential scanning calorimetric analysis. The parameters from these models of curves allow us to evaluate the enthalpies, and the degree of progression of this blended cement, and finally determine their activation energies. We can say that the hydration of Portland cement is due to a series of reactions as （ C3S,C2S,C3A and C4AF reactions with water） and each of them, has its own kinetic, the experimental measurement of the heat of hydration, allows us to represent the overall kinetics of these reactions values of activation energy, they are therefore apparent and global energy. In our experiments, significant differences in these physicochemical parameters were observed, depending on the additive used.

Use of Magnesium Oxide-cement Binder in Composites Based on Hemp Shives

In this paper, it presented the results of experimental study of utilization of MgO cement as calcium hydrate replacement in lightweight composites based on hemp shives. The results of selected characteristics （compressive strength and coefficient of thermal conductivity） of hardened composites show that MgO cement based on the milled caustic magnesite is suitable alternative in comparison to conventional binders used in hemp concrete. This material leads to new environmentally products as non-load bearing building materials.

Hydrothermal activities and seawater acidification in the Late Devonian F-F transition:Evidence from geochemistry of rare earth elements

Rare-earth dements （REE） in limestones were measured by ICP-MS from the Yangdi section across the Frasnian-Famennian （F-F） transition in Guilin, Guangxi of South China. The average EREE contents of measured samples are 33.32 ppm. The average LREE/HREE ratio is 6.35. Data show LREE-enriched REE distribution pattern in the Yangdi section. Most of samples are characterized by positive Eu anomaly with average of 1.13, and there are two maxima of Eu anomaly just below the F-F boundary. Almost all analytical samples show obvious tetrad effects. Remarkable M-shaped tetrad effects are observed in these samples with positive Eu anomaly. The characters of REE and some relative elements （Fe, Mn, Al, etc.） indicate that hydro- thermal activities occurred and resulted in seawater acidification in Upper and Lower Kellwasser horizons of the Late Devonian. The changes of marine environment caused by hydrothermal activities, such as seawater acidification, heavy metal pollution, and eutrophication, would destroy the neritic ecosystem and finally result in the F-F mass extinction.