A Simple Cement Hydration Model Considering the Influences ofWater-to-Cement Ratio and Mineral Composition

A simple hydration model is used here by taking the composition of the cement and the initial water: cementratio (w/c) into account explicitly. Its conceptual basis is a combination of the Avrami equation and Bentz’s modelbased on simple spatial considerations. In this model, the Avrami equation determines the initial reaction, andBentz’s model describes the following hydration stage. The model favors engineers for it relies on one experimentalparameter and has a reliable approximation in the practice.

Effects of porosity,dry unit weight,cement content and void/cement ratio on unconfined compressive strength of roof tile waste-silty soil mixtures

One of the conventional ways to improve the mechanical behavior of soils is to mix them with cementing agents such as cement, lime and fly ash. Recently, introduction to alternative materials or sub-products that can be adopted to improve the soil strength is of paramount importance. Therefore, the present study aims to investigate the effects of porosity(h), dry unit weight(gd) of molding, cement content(C)and porosity/volumetric cement content ratio(h/Civ) or void/cement ratio on the unconfined compressive strength(quor UCS) of silty soileroof tile waste(RT) mixtures. Soil samples are molded into four different dry unit weights(i.e. 13 kN/m^3, 13.67 kN/m^3, 14.33 kN/m^3 and 15 kN/m^3) using 3%, 6% and 9%cement and 5%, 15% and 30% RT. The results show that with the addition of cement, the strength of the RT esoil mixtures increases in a linear manner. On the other hand, the addition of RT decreases quof the samples at a constant percentage of cement, and the decrease in porosity can increase qu. A dosage equation is derived from the experimental data using the porosity/volumetric cement content ratio(h/C_(iv)) where the control variables are the moisture content, crushed tile content, cement content and porosity.

Influence of MgO/MgCl_2 Molar Ratio on Phase Stability of Magnesium Oxychloride Cement

Formation, solution and phase change of hydration products in MgO-MgCl2-H2O system was studied with thermodynamics method, and resistance to water immersion and phase change of magnesium oxychloride cement with different MgO/MgCl2 molar ratio was experimented. The results show that pH value of immersion solution of cement paste has a remarkable influence on phase stability of hydration products. A higher pH value leads to a lower solubility and a better phase stability of hydration products. When the solution pH value is higher than 10.37, the precipitation of much Mg（OH）2 crystal induces a worse phase stability of hydration products. With the increasing MgO/MgCl2 molar ratio （lower than 6）, the more amount of MgO in the hydration products enhances the alkalinity of solution and the phase stability is improved. However, when the MgO/MgCl2 molar ratio is higher than 6 and the excessive MgO exsits in the hydration products, the cement paste may be damaged by the excessive crystallization stress of a great deal of Mg（OH）2 formation.

The Hydration of Blended Cement at Low W/B Ratio

The hydration process,hydration product and hydration heat of blended cement paste mixed with mineral admixture and expansive agent at low W/B ratio are studied by XRD,thermo analysis,and calorimetry instrument,and they were compared with those of pure cement paste.The results show that pure cement and blended cement at low W/B ratio have the same types of hydration products,but their respective amounts of hydration products of various blended cements at same ages and the variation law of the amount of same hydration products with ages are different;The joint effect of tumefaction of gel-ettringite due to water absorption and the expansive pressure on the pore and rift caused by the crystalloid ettringite is the impetus of the volume expansion of cement paste,and the former effect is much greater than the latter one.

Form and Mechanism of Sulfate Attack on Cement-based Material Made of Limestone Powder at Low Water-binder Ratio under Low Temperature Conditions

The development of strength and the form of attack of cement-based material made of limestone powder at low water-binder ratio under low-temperature sulfate environment were studied. The results indicate that when water-binder ratio is lower than 0.40, the cement-based material with limestone powder has insignificant change in appearance after being soaked in 10% magnesium sulfate solution at low temperature for 120 d, and has significant change in appearance after being soaked at the age of 200 d. Expansion damage and exfoliation occur on the surface of concrete test cube at different levels. When limestone powder accounts for about 28 percent of cementitious material, with the decrease of water-binder ratio, the compressive strength loss has gradually decreased after the material is soaked in the magnesium sulfate solution at low temperature at the age of 200 d. After the specimen with the water-binder ratio of less than 0.4 and the limestone powder volume of greater than 20% is soaked in 10% magnesium sulfate solution at low temperature at the age of 200 d, gypsum attack-led destruction is caused to the concrete test cube, without thaumasite sulfate attack.

Influence of zeolite and cement additions on mechanical behavior of sandy soil

It is well known that the cemented sand is one of economic and environmental topics in soil stabilization. In this instance, a blend of sand, cement and other materials such as fiber, glass, nanoparticle and zeolite can be commercially available and effectively used in soil stabilization in road construction. However, the influence and effectiveness of zeolite on the properties of cemented sand systems have not been completely explored. In this study, based on an experimental program, the effects of zeolite on the characteristics of cemented sands are investigated. Stabilizing agent includes Portland cement of type II and zeolite. Results show the improvements of unconfined compressive strength （UCS） and failure properties of cemented sand when the cement is replaced by zeolite at an optimum proportion of 30% after 28 days. The rate of strength improvement is approximately between 20% and 78%. The efficiency of using zeolite increases with the increases in cement amount and porosity. Finally, a power function of void-cement ratio and zeolite content is demonstrated to be an appropriate method to assess UCS of zeolite-cemented mixtures.

Characterisation of Early Age Deformations in Cement Paste: Case of Chemical and Autogenous Shrinkage

Concrete is commonly seen as a durable and long-lasting construction material. However, the long-term performance of a concrete structure can be greatly compromised by early-age cracking. This work is an experimental contribution to study early age deformations of cement paste. Its aim is, firstly, to develop an experimental dispositive for assessing chemical and autogenous shrinkage, and secondly, to measure these volumetric deformations in cement paste. The setup was done following the gravimetric method of measurement, which exploits the Archimedes’ principle. It is made up of an electronic balance, a data accusation unit, a temperature control unit and a buoyancy bath. Investigations were done on Portland cement (CPA-CEM II) at the following W/C ratios: 0.25, 0.3, 0.35, 0.4 and 0.5. It was noticed that the water-cement ratio does not influence the magnitude of the chemical shrinkage in a significant manner but had a kinetic effect;a lower W/C induces a faster rate of chemical shrinkage. Autogenous shrinkage was discovered to be highly inversely proportional to the W/C and was also noticed to be in a function of chemical shrinkage within the first 2 to 4 hours when the paste was still liquid.

Assessment of strength development in cement-admixed artificial organic soil with GX07

To explore the stabilization effect of stabilizing agent GX07 on treating organic soil and the influence of organic matter on the strength development of stabilized soil,artificial organic soil with various organic matter content was obtained by adding different amounts of fulvic acid into non-organic clay,and then liquid-plastic limit tests were carried out on the artificial organic soil.Meanwhile,unconfined compressive strength(UCS) tests were performed on cement-only soil and composite stabilized soil,respectively.The test results indicate that the plastic limit of soil samples increases linearly,and the liquid limit increases exponentially as the organic matter content increases.The strength of stabilized soil is well correlated with the organic matter content,cement content,stabilizing agent content and curing time.When the organic matter content is 6%,as the cement content varies in the range of 10%-20%,the strength of cement-only soil increases from 88.5 to 280.8 kPa.Once 12.6% GX07 is added into the mix,the strength of stabilized soil is 4.93 times compared with that of cement-only soil.GX07 can obviously improve the strength of cemented-soil and has a good economic applicability.A strength model is proposed to predict strength development.

Experimental Study on Chloride Ion Penetration Resistance of Coal Gangue Concrete under Multi-Factor Comprehensive Action

In order to investigate the chloride ion penetration resistance of coal gangue concrete under multi-factor comprehensive action, the non-steady-state accelerated chloride ion migration test was used to test the chloride diffusion law of coal gangue concrete specimens by crack width, curing temperature and water-cement ratio. Three groups of crack width (0 mm, 0.05 - 0.12 mm, 0.12 - 0.2 mm), three curing temperatures (high temperature 45, medium temperature 25, low temperature 10), three water cement ratios (0.3, 0.4, 0.5) were set in the experiment. The results show that when the curing temperature and water cement ratio are constant, the crack width less than 0.12 mm has little effect on the chloride content and chloride diffusion coefficient. When the crack width is larger than 0.12 mm, the chloride penetration depth increases with the crack width. The resistance to chloride ion penetration of gangue concrete is greatly influenced by the water cement ratio. The influ-ence degree of three factors on chloride ion migration coefficient of gangue concrete is as follows: water cement ratio > crack width > curing temperature.

Packing Density Improvement through Addition of Limestone Fines, Superfine Cement and Condensed Silica Fume

Adoption of a low water/powder (W/P) ratio is the key to improve the strength and durability of concrete, which relies on a high packing density because fresh concrete requires excess water to offer flowability. To obtain a high packing density, powders with different particle sizes, including limestone fines (LSF), superfine cement (SFC), condensed silica fume (CSF), were added to the cement paste and the resulting packing densities were measured directly by a newly-developed wet packing test. Results demonstrated that addition of powders with a finer size would more significantly improve the packing density but the powders should be at least as fine as 1/4 of the OPC to effectively improve the packing density. Packing density and voids ratio relationship showed that a small increase in packing density can significantly decrease the voids ratio, which could allow the W/P ratio to be reduced to improve the strength and durability of the concrete without compromising the flowability.

Effects of binder strength and aggregate size on the compressive strength and void ratio of porous concrete

To test the influence of binder strength, porous concretes with 4 binder strengths between 30.0-135.0 MPa and 5 void ratios between 15%-35% were tested. The results indicated that for the same aggregate, the rates of strength reduction due to the increases in void ratio were the same for binders with different strengths. To study the influence of aggregate size, 3 single size aggregates with nominal sizes of 5.0, 13.0 and 20.0 mm （Nos. 7, 6 and 5 according to JIS A 5001） were used to make porous concrete. The strengths of porous concrete are found to be dependent on aggregate size. The rate of strength reduction of porous concrete with small aggregate size is found to be higher than that with larger aggregate size. At the same void ratio, the strength of porous concrete with large aggregate is larger than that with small aggregate. The general equations for porous concrete are related to compressive strength and void ratio for different binder strengths and aggregate sizes.

Effect of W/C ratio and cover thickness on polarization characteristics of embedded steel in mortar

The effects of cover thickness and W/C(water-to-cement) ratio on polarization properties of embedded steel bar were investigated with electrochemical methods.Corrosion potentials shift to the noble direction with increasing the cover thickness.In addition,when the cover thickness increasingly becomes thinner and thinner,effect of the W/C ratio on variation of corrosion potential increases as well.Impedance value at 100 kHz indicating the resistance of cover thickness increases with the decrement of W/C ratio as well as the increment of cover thickness.However,in the case of W/C ratio at 0.6,impedance at 10 mHz shows the relatively larger value than that at W/C ratio of 0.4 or 0.5 in the range of cover thickness from 4 to 8 cm,which is probably expected that oxide film built up on the surface of steel bar due to strong alkali environment by hydration reaction with increasing W/C ratio is performed as the resistance polarization.It is also observed that liquid junction potential tends to increase with decreasing W/C ratio.

Development of a Laboratory Cement Quality Analysis Apparatus Based on Laser-Induced Breakdown Spectroscopy

Determination of the chemical composition of cement and ratio values of clinker plays an important role in cement plants as part of the optimal process control and product quality evaluation. In the present paper, a laboratory laser-induced breakdown spectroscopy （LIBS） apparatus mainly comprising a sealed optical module and an analysis chamber has been designed for possible application in cement plants for on-site quality analysis of cement. Emphasis is placed on the structure and operation of the LIBS apparatus, the sealed optical path, the temperature controlled spectrometer, the sample holder, the proper calibration model established for minimizing the matrix effects, and a correction method proposed for overcoming the ＇drift＇ obstacle. Good agreement has been found between the laboratory measurement results from the LIBS method and those from the traditional method. The absolute measurement errors presented here for oxides analysis are within 0.5%, while those of ratio values are in the range of 0.02 to 0.05. According to the obtained results, this laboratory LIBS apparatus is capable of performing reliable and accurate, composition and proximate analysis of cement and is suitable for application in cement plants.

Effect of Curing Regime on Polymerization of C-S-H in Hardened Cement Pastes

The effect of two different curing regimes on the polymerization degree of C-S-H in hardened cement pastes within 28 d were investigated by measuring the chemical environments of 29Si with magic angle spinning （MAS） nuclear magnetic resonance （NMR） and by analyzing the 29Si NMR spectra with deconvolution technique. The experimental results indicate that, at curing regime of constant temperature of 20℃, the polymerization of C-S-H increases and then decreases with curing age, and the A1/Si ratio increases gradually with curing age, furthermore, the two non-bridging oxygen bonds of bridging silicate tetrahedra in C-S-H structure mainly bond to H＋. At curing regime of variable temperature, the polymerization of C-S-H firstly increases then changes slightly and subsequently decreases with the temperature from low to high and then to low, and the A1/Si ratio firstly increases then keeps invariant and subsequently slightly decreases. Moreover, the temperature decreasing is advantageous for the Ca2＋ to be bonded to the bridging silicate tetrahedra and entering into the interlayer of C-S-H structure. The polymerization of C-S-H at curing regime of variable temperature is higher than that cured at constant temperature, but the curing regime of constant temperature is more beneficial to the substitution of AP for Si4＋ than that of variable temperature.

煤矸石机制砂C20混凝土力学性能研究

为探究煤矸石机制砂对低强度等级C20混凝土力学性能的影响,调控煤矸石机制砂掺量和水灰比浇筑混凝土试块,开展抗压和抗折强度试验。结果表明:相同水灰比下,随煤矸石机制砂掺量增加,混凝土的抗压强度先增强后降低;相同取代率下,混凝土的抗压和抗折强度随水灰比增大而降低。相较于煤矸石机制砂取代率,水灰比对混凝土抗折强度的影响更大。取代率不超过30%时,对混凝土的抗压和抗折强度均有利,水灰比为0.55、取代率为25%时,混凝土抗压和抗折强度提高最多。

Dynamic properties of composite cemented clay

In this work, the dynamic properties of composite cemented clay under a wide range of strains were studied considering the effect of different mixing ratio and the change of confining pressures through dynamic triaxial test. A simple and practical method to estimate the dynamic elastic modulus and damping ratio is proposed in this paper and a related empirical normalized formula is also presented. The results provide useful guidelines for preliminary estimation of cement requirements to improve the dynamic properties of clays.

原生混凝土强度对再生骨料透水混凝土强度的影响

将废弃混凝土试块按强度等级分类制成再生骨料,在不同水灰比条件下制备再生骨料透水混凝土。通过对所制试件进行抗压强度和弯拉强度测试、宏观和微观组织表征以及显微硬度测试,分析了原生混凝土强度和水灰比对再生骨料透水混凝土强度的影响。结果表明,再生骨料透水混凝土强度与原生混凝土强度存在明确正相关性。原生混凝土强度每提高10 MPa,再生骨料透水混凝土抗压强度可提高10%~20%,弯拉强度可提高10%~30%。不同强度等级原生混凝土制备的再生骨料透水混凝土最优水灰比呈现规律性变化。随着原生混凝土强度的提高,再生骨料表面的孔隙变小、微裂缝变少,附着的水泥浆趋于致密,所制再生骨料透水混凝土界面强度增大。

透水混凝土力学性能影响因素的研究进展与分析

为保证工程建设的安全性和有效性,充分了解不同因素对透水混凝土力学性能的影响机理,总结了近年来国内外关于水灰比、砂率、掺合料种类及掺量、骨料粒径等因素对透水混凝土力学性能影响的研究成果,分析了现有研究中存在的不足和尚未解决的问题,并基于透水混凝土细观损伤机理和力学行为,指出了未来进一步研究方向。

镁硅比和养护温度对硅酸镁水泥电磁性能的影响

采用波导法测定硅酸镁水泥的电磁性能,分析镁硅比和养护温度的影响,并基于微观测试结果进行机理分析.结果表明:提高养护温度可以显著增强硅酸镁水泥的早期强度;硅酸镁水泥的复介电常数实部随着镁硅比和养护温度的提高逐渐增大;提高养护温度使硅酸镁水泥的复介电常数虚部和损耗角正切值增大;与镁硅比相比,养护温度对硅酸镁水泥的透射率、反射率和吸收率的影响更为明显.微观测试结果显示含水量和孔结构对硅酸镁水泥的电磁性能有重要影响.

Potentials of <i>Bambusa vulgaris</i>Grown in Southeast Nigeria for the Manufacture of Wood-Cement Composite Panels

In this work, the potentials of Bambusa vulgaris grown in southeast Nigeria for the manufacture of wood-cement composite panels were studied. Representative culms of Bambusa vulgaris were collected from a 4-year-old stand at lower Anambra river basin, southeast, Nigeria. Fiber morphological properties and proximate chemical analysis were determined in accordance with the provisions of the Technical Association of the Pulp and Paper Industries (TAPPI, 1998). Fiber slenderness ratio was 160.95:1, component solubility of 3.09, 5.60, and 19.8 percent for cold water soak for 24 hrs;hot water soak at 80°C for 1 hr, and 1% NaOH soak for 24 hrs respectively. Composite panels were made at 1200 kg/m3 and 800 kg/m3 density levels with flakes of different soak treatments (untreated/control;cold water soak for 24 hrs;water at 80°C soak for 1 hr and 1% NaOH soak for 24 hrs) at variable cement/B. vulgaris mix ratios (1:1, 1.5:1, 2:1, 2.5:1 and 3:1 wt/wt) with 3% CaCl2 as accelerator applied to the wood furnish before cement mixing. Prepared furnish was subjected to initial pre-pressing of 0.5 N/mm2 and final consolidation of 1.4 N/mm2 retained for 24 hrs. Panels were sampled and tested after 28 days for Modulus of Rupture (MOR) and Modulus of Elasticity (MOE) in bending and for water absorption (WA) and thickness swelling (TS) due to a 24-hr water soak. Test was in accordance with provisions of American Standard for Testing of Materials (ASTM-1998). Properties ranged from a low of 25.00 to 75.45 N/mm2 for MOR;4128 to 15,065 N/mm2 for MOE;15.01 to 36.11 percent for WA and 3.04 to 12.72 percent for TA. Effect of production mix on properties was determined using factorial analysis. Except for composite density whose effect was not significant at 0.05% level, all production mix was found significant at 0.01% level at the second order level of interactions. All panels met minimum property requirements of American National Standard Institute 208-2-1994 and 208-1-1993, British Standard (BS 5669, 1979) and Malaysian Standard (MS 934, 1984).