高性能混凝土在广州地铁中的应用

本文探讨粉煤灰高性能混凝土在广州地铁中的应用，通过不同配比情况下高性能混凝土强度，抗渗性试验以及实际应用情况的研究，分析了影响高性能混凝土性能的各种外加剂和掺合料因素及其适用范围，并提出了在实际地铁施工中使用高有混凝土应注意问题。     

电渗法在混凝土耐久性研究中的应用进展

电渗法是指采用外电场加速带电离子在混凝土中的渗透迁移,常用在混凝土耐久性研究中.对电渗法在研究氯离子渗透性、延长混凝土的使用寿命、钢筋阻锈剂评价3个方面的应用进行了详细的介绍.最后对各种电渗法进行了客观评价.     

YJH材料性能及其对混凝土微观结构的影响

为研究YJH渗透结晶材料性能及其对混凝土微观结构的影响,通过在混凝土表面使用不同涂料用量及养护不同时间,分析测试了不同涂层试件的抗渗性能和自修复性能,并通过SEM研究了YJH渗透结晶型材料对水泥砂浆试件微观结构的影响.结果表明:防水涂层可通过催化作用促使未水化的水泥再产生新的晶体,堵塞砂浆孔隙,提高水泥混凝土的抗渗性能,并赋予其自修复功能;当涂料用量为1 kg/m2时,可使水泥混凝土基体的28 d抗渗性能由0.4 MPa提高到1.4 MPa,二次抗渗仍可达到1.2 MPa;涂料的催化结晶作用是长期有效逐渐进行的,经YJH涂料进行涂层处理的水泥混凝土的养护时间越长,其微观结构越密实,防水抗渗性能越好.     

框架结构设计的要点和过程

1结构设计说明 主要是设计依据，抗震等级，人防等级，地基情况及承载力，防潮抗渗做法，活荷载值，材料等级，施工中的注意事项，选用详图，通用详图或节点，以及在施工图中未画出而通过说明来表达的信息。如混凝土的含碱量不得超过3kg／m^3等等。     

混凝土抗渗仪检测方法的改进

0引言 混凝土是建筑工程中被广泛应用的一种石材,在水工、地下及其他建筑工程中,要求混凝土构筑物具有特殊性能、抗渗性能。混凝土抗渗仪主要用于硬化后混凝土抗渗标号的测定试验,在建筑领域应用极为普遍。但对其检定,还未出台相应的国家检定规程。目前,国内计量检定部门大都结合建筑行业SL352—2006《水工混凝土试验规程》中的相关要求,对混凝土抗渗仪主要开展四个项目的检测：1）混凝土抗渗仪压力和控制部分指标的检定;2）混凝土抗渗仪供压管道的密封性指标测试;3）混凝土抗渗仪试模尺寸指标的检测;4）混凝土抗渗仪绝缘电阻的检测。     

混凝土抗渗仪测得值的不确定度评定

抗渗仪是测定混凝土的抗渗性能,适用于建筑企业、科研院校、设计施工等部门从事混凝土抗渗性能的测定研究,同时可用于其它建筑材料透气测定和质量检测。本文分析测量不确定度的来源,对各不确定度进行详细评定,并给出示值误差的不确定度。     

浅议水利工程混凝土建筑物的抗渗性

[摘要]介绍渗漏对水工混凝土带来的一系列恶性循环危害、影响水工混凝士抗渗性的因素及抗渗性对水工混凝土耐久性的影响等，阐明水工混凝土抗渗性研究的重要性。     

混凝土强度不足事故的处理

混凝土强度不足时，除了影响结构的承载能力，还会降低混凝土的抗渗性能及耐久性．处理这类事故的前提是必须明确处理的主要目的，如为提高承载能力，可采用一般加固补强方法处理；如果因为混凝土密实性差等内在原因，造成抗渗、抗冻、耐久性差，则主要应从提高混凝土密实度或增加强度、抗渗、抗冻、耐久性能等方面着手进行处理。     

石粉对水泥-矿粉混凝土性能的影响

本文主要研究了石粉对水泥-矿粉混凝土的工作性、抗压强度、耐久性能(抗渗性能、抗碳化性能和抗冻性能)的影响,并利用孔结构微观分析对其进行了机理分析。研究表明:石粉应用于水泥-矿粉混凝土中,不仅可改善混凝土的工作性能,而且可提高混凝土的抗压强度,对混凝土的耐久性能(抗渗性能、抗碳化性能和抗冻性能)影响不大。     

再生混凝土纳米复合强化试验

本文对再生混凝土进行纳米复合强化试验研究,通过引入高活性纳米SiO2和纳米改性矿物掺合料,得到了纳米改性再生混凝土,研究了高活性纳米SiO2和纳米改性矿物掺合料对再生混凝土力学性能的影响,还研究了高活性纳米SiO2对再生混凝土抗氯离子渗透性能与抗渗性能的影响,为实际工程应用提供理论依据。研究结果表明:纳米SiO2与纳米改性矿物掺合料双掺,不仅能在一定程度上改善再生混凝土的力学性能,还能显著改善再生混凝土的抗氯离子渗透性能与抗渗性能,显示出良好的复合效果。     

Application of some nuclear and radiographic methods on concrete

Some nuclear and radiographic techniques used for the study of concrete are described. Gamma-ray transmission method was used for studying the variation in density of concrete caused by settling in columns. Moisture content of concrete was determined by the neutron scattering technique and the distribution of cement was studied by radioactive tracer analysis. A judicious use of such methods can provide information necessary for an engineering analysis of many problems. The structure of concrete was studied by radiographing thin slices of concrete. Formation and propagation of cracks was studied from radiographs taken at regular intervals.     

Some factors influencing air permeation measurements in cover concrete

The report concerns a method of measuring the apparent air permeability in cover concrete and the effects of air flow geometry, cracks and concrete moisture conditions. The method involved pressurizing a 20 mm diameter cavity cut 35 mm deep into the concrete and measuring the rate of pressure decay. A positive testing pressure coupled with the application of liquid soap solution permitted direct observation of air permeation as bubbles. The depth of the cavity was a critical factor and it was desirable to locate the cavity so that its centre-line was at least 40 mm from the nearest lateral surface. Cracks in the concrete increased the permeability and the variability of results. Pore water restricted air permeation through the cover concrete. Moisture conditions were conveniently monitored using a relative humidity probe in the cavity and by measuring weight losses during drying and wetting.     

Long term durability of pultruded polymer composite rebar in concrete environment

Pultruded glass fibre reinforced polymer (GFRP) composite rebar was immersed in alkaline concrete environment for 0, 1, 2, 3, 4, 6, 14 and 24 months at 60 °C to evaluate its durability in concrete structure. Moisture absorption of the rebar was found to be only 0.76%. It was also found that both the glass transition temperature (T_g) and the short beam shear strength were retained by about 91.5%; and the above properties were remained almost unchanged during the ageing period from 1 month to 24 months. Design tensile strength and tensile elastic modulus of the rebar were retained by 100% after 24 months exposure in concrete environment. Degradation of GFRP rebar was not evident in the FT-IR results as supported by scanning electron micrographs and energy dispersive X-ray analysis. Moisture absorption was found to be a critical factor that controlled thermal and mechanical properties of GFRP rebar.     

Corrosion monitoring of steel in concrete by galvanostatic pulse technique

Various non-destructive quantitative techniques based on electrochemical methods for measuring the corrosion rate of steel embedded in concrete have been used. The most important is the linear polarization method. In practice, this method gives lower corrosion rates of steel in concrete due to inclusion of the resistance of the concrete in the measurement. In order to eliminate the resistance of the concrete, a galvanostatic pulse method is used. In this method the current pulse is applied to the steel in concrete and the polarizing potential is sampled after the switching off the pulse. The performance of the galvanostatic pulse technique for monitoring the corrosion of steel in concrete has been assessed by comparing the corrosion rate values obtained by the weight loss method and linear polarization resistance method for steel reinforced in M15, M20, M30 and M35 grade concrete containing 0–5% NaCl. It is found that the galvanostatic pulse technique is able to give reliable corrosion rate values of steel in concrete.     

Social media for health promotion: A visual analysis of “TB proof” South Africa's Facebook page

Health promotion is an educational tool that can be used to educate and create awareness of health issues through various media forms. The purpose of this study was to explore the use of social media (TB Proof South Africa's Facebook page) in creating tuberculosis (TB) awareness. A qualitative case study approach was used to collect data from TB Proof South Africa's Facebook page. An in-depth visual analysis of TB Proof South Africa's Facebook page was carried out over a five-month period (from 1 February to June 30, 2017). The analysis of TB Proof South Africa's Facebook page was conducted in order to determine the use of social media for health promotion. Such a comprehensive analysis was aimed at determining if the visuals on this page create awareness on TB as an illness. Common themes were identified including, TB medication, TB patients and healthcare workers raising awareness on TB. The findings have potential implications for health promotion efforts using social media.     

Strength evaluation of recycled-aggregate concrete byin-situ tests

Coarse and fine aggregates generated from crushed concrete products for new concrete can be generally accepted only when the properties of recycled aggregate concrete, in addition to the relationships between different properties of such a concrete, are well understood. The results of an experimental investigation into the relationship of compressive strength to ultrasonic pulse velocity and to rebound number is presented in this paper. It has been observed that for the water-cured concrete the strength-pulse velocity relationship is influenced by the use of the recycled aggregate. For the same value of the pulse velocity, the strength of recycled aggregate concrete is higher than that for the natural aggregate concrete. On the other hand, the strength-rebound number relationship is not affected by the aggregate type used. The combined method of pulse velocity and rebound number for strength estimation is also evaluated.     

Interactive Effects of Fly Ash and CNI on Corrosion of Reinforced High-Performance Concrete

The interactive effects of fly ash and CNI in corrosion of reinforced concrete were investigated. A 3⁴ full factorial design was developed considering water to cement ratio, fly ash percent, CNI and cracked condition as factors. The response factors were the weight loss calculated from Linear Polarization Resistance measurements and the pit depth of the steel bars embedded in concrete. Small-scale concrete slabs containing steel reinforcement with a cover depth of 20 mm were cast for this purpose. The slabs were subjected to a simulated marine environment with two cycles of wetting and drying per day during one year; after the exposure, the slabs were broken, the bars were cleaned and the pith depth measured by using SEM. Under the studied conditions, it was found that CNI alone does not provide corrosion protection of the steel reinforcement even for uncracked silica fume concrete in a 0.45 w/c ratio; however, the combination of CNI and fly ash can be useful to overcome this problem. The results indicate that low w/c ratio concrete in its crack state creates conditions suitable for the development of pitting corrosion.     

Effect of hot weather on pulse velocity and modulus of elasticity of concrete

This paper presents the results of tests for pulse velocity and modulus of elasticity conducted on concrete specimens prepared and cured under both controlled laboratory conditions and natural atmospheric conditions of hot weather. The results have shown that both the pulse velocity and modulus of elasticity of concrete are reduced with increase in concrete mix temperature at preparation, indicating the detrimental effect of hot weather on the quality of concrete. Even if the concrete mix is so designed as to give the required compressive strength for concrete prepared and cured in hot weather, the modulus of elasticity could be reduced by as much as 17.5%.     

Drying induced moisture losses from mortar to the environment. Part I: experimental research

Moisture conditions in the pore structure of hardening cementitious materials are known to have determinant influence on the onset and continuance of hydration reactions. Moisture loss from regions near exposed surfaces may jeopardize the quality of concrete cover in terms of both mechanical and durability issues. In addition, drying shrinkage, a phenomenon directly related to a moisture loss to the environment, is known to be responsible for several surface cracks that impair durability performance and pose aesthetical problems. Furthermore, evaporative cooling that occurs in concrete surfaces in the first minutes just after formwork removal may cause thermal cracking. For the above mentioned reasons, it is important to assess the mechanisms of moisture losses from cement-based materials to the environment, in order to rationally establish curing criteria. This paper describes an experimental campaign conducted with the purpose of better understanding the effect of various environmental conditions on the referred moisture interactions, accounting for influences such as the environmental temperature, the relative humidity (RH), the wind speed and direction, as well as the duration of curing. Numerical simulations with comparisons against test data, as well as some sensitivity analyses, are relegated to the companion paper that follows in this issue.     

In Vitro and In Vivo Evaluation of Two Extended Release Preparations of Combination Metformin and Glipizide

A system that can deliver multi-drugs at a prolonged rate is very important to the treatment of various chronic diseases such as diabetes, asthma, and heart disease. Two controlled-release systems, which exhibited similar release profiles of metformin and glipizide, i.e., elementary osmotic pump tablets (EOP) and bilayer hydrophilic matrix tablet (BT), were designed. The effects of pH and hydrodynamic conditions on drug release from two formulations were investigated. It was found that both drug releases from EOP were not sensitive to dissolution media pH and hydrodynamics change, while the release of glipizide from BT was influenced by the stirring rate. Moreover, in vivo evaluation was performed, relative to the equivalent dose of conventional metformin tablet and glipizide tablet, by a three-crossover study in six Beagle dogs. Cumulative percent input in vivo was compared to in vitro release profiles. The linear correlations of metformin and glipizide between fraction absorbed in vivo and fraction dissolved in vitro were established for EOP—a true zero-order release formula, whereas only nonlinear correlations were obtained for BT. In conclusion, drug release from EOP was both independent of in vitro and in vivo conditions, where the best sustained release effect was achieved, whereas the in vitro dissolution test employed for BT needed to be further optimized to be biorelevant.