瞬态高温对重量级高强度混凝土的影响外文翻译资料

 2022-08-19 15:35:46

EFFECT OF TRANSIENT HIGH TEMPERATURE ON HEAVYWEIGHT, HIGH

STRENGTH CONCRETE

M. Mahdy1, P.R.S.Speare 2, and A. H. Abdel-Reheem 3

ABSTRACT

As the use of special high strength concrete becomes necessary for special purpose, the risk of exposing it to high temperatures also increases. To be able to predict the response of structures employing special high strength concrete after exposure to high temperature, it is essential that the strength properties of special high strength concrete subjected to high temperatures be clearly understood.

In the present work, 12 mixes were selected to achieve a slump above 100 mm and strength up to 140 MPa at 180 days. To achieve this a 0.24 water/cement ratio and 3.5% super plasticiser were used. The investigation used three levels of silicafume (0, 10%, 20% by weight of cement), two coarse aggregate proportions of total aggregate (0.48, 0.65 by volume) and both magnetite and natural sand fine aggregate were used. The effect of transient high temperature on strength of heavyweight high strength concrete was investigated. There were three exposure durations (0, 1hr, 2hrs.)at temperatures of 100, 300, 500 and 700 °C. As the temperature increased to 100 °C, the strength decreased compared to the room temperature strength. With further increase in temperature, the specimens recovered the strength loss and reached a peak strength of 10 to 30 % above the room temperature strength. At the temperature 500 and 700 °C, the strength in each case dropped sharply.

Keywords: heavyweight concrete, high strength concrete; magnetite concrete; heavyweight aggregate; high temperature; elevated temperature; compressive strength.

INTRODUCTION

For shielding from gamma rays and X-rays the density of the concrete is the most important parameter and increasing the density leads to reduced thickness of concrete required. Thermal stresses are generated either by external sources of heat as, for example, in the case of shields for nuclear reactors, or from heat arising from the attenuation or absorption of gamma and neutron radiation within the shield. Davis (1) pointed out that in most shielding structures stresses due to thermal effects or thermal loads could be of greater importance than stresses due to mechanical or non-thermal loads on the structure.

Three types of tests are commonly used to study the effect of transient high temperature on

1 Mansoura University, El-Mansoura, Egypt. E-mail: mmahdy@mum.mans.eun.eg

2 School of Engineering, City University, London, UK. E-mail: P.R.S.Speare@city.ac.uk

3 Dept. of Structural Eng., Mansoura University, El-Mansoura, Egypt.

the stress strain properties of concrete under axial compression:

1- Unstressed tests, where the specimens are heated under no initial stress and loaded to failure at the desired elevated temperature.

2- Stressed tests, where a fraction of the ultimate compressive strength at room temperature is applied and sustained during heating and, when the target temperature is reached, the specimens are loaded to failure.

3- Residual unstressed tests, where the specimens are heated without any load, cooled down to room temperature and then loaded to failure.

In general, the residual unstressed strength is lower than the unstressed strength (2, 3). As temperature is increased, normal strength concrete initially experiences a 10% loss in strength up to a temperature of 125 °C. This is followed by a gain of strength of as much as 15% of the room temperature strength, up to 250 °C. With further increase in temperature, the strength drops rather rapidly, falling to as little as 20 percent of the original strength at 700 °C (4, 5). The moisture content at the time of testing has a significant effect on the strength of concrete at elevated temperature. Tests on sealed and unsealed specimens have shown that higher strength is obtained if moisture is allowed to escape (6, 7).

RESEARCH SIGNIFICANCE

With increasing use of high strength concrete, the risk of exposure to high temperatures has also increased. To be able to assess the structural safety of such structures after exposure to high temperature, it is important that the effect on strength be well understood. This paper provides initial findings of an ongoing study on the behavior of heavy weight high strength concrete under extreme temperature conditions.

OBJECTIVE AND SCOPE

The main objective of this investigation was to study the effect of transient high temperature on compressive strength of heavy weight high strength concrete and compare the behavior with that of heavy weight normal strength concrete. The test specimens were subjected to temperatures ranging from 100 to 700 °C and their behavior compared to that observed at room temperature.

EXPERIMENTAL PROGRAME

Materials

Detailed information about the materials used and their characteristics are given in this section. Cement Portland cement has been found to be adequate for production of high strength concrete. Experience has indicated that PC is, in most cases, entirely satisfactory and adequate for constructing concrete shielding

Mineral admixtures. Silica fume slurry (sf) was used in this programme and particular care was taken over curing since the pozzolanic reaction takes place over a longer time.

Aggregate Magnetite was used as both coarse aggregate and, in some mixes, as fine aggregate as well. This is in line with ASTM C638 and the grading was chosen to conform with the requirements of ASTM C637-84 for radiation shielding concrete. The coarse aggregate had a maximum size of 16 mm and the typical chemical analysis was Fe 62 %, SiO2 3.6 %, MgO 1.2 %, Al2O3 0.5 %. The specific gravity was

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EFFECT OF TRANSIENT HIGH TEMPERATURE ON HEAVYWEIGHT, HIGH

STRENGTH CONCRETE

瞬态高温对重量级高强度混凝土的影响

M. Mahdy1, P.R.S.Speare 2, and A. H. Abdel-Reheem 3

Mahdy1先生,P.R.S.Speare 2、3和Abdel-Reheem a.h.先生

ABSTRACT

摘要

As the use of special high strength concrete becomes necessary for special purpose, the risk of exposing it to high temperatures also increases. To be able to predict the response of structures employing special high strength concrete after exposure to high temperature, it is essential that the strength properties of special high strength concrete subjected to high temperatures be clearly understood.

为了特殊目的使用特殊的高强混凝土成为必要，但同时暴露在高温下的风险也会增加。采用特殊高强混凝土，暴露在高温后能够预测结构的响应,其中至关重要的是,能清楚地理解受到高温影响后特殊的高强混凝土的强度性能。

In the present work, 12 mixes were selected to achieve a slump above 100 mm and strength up to 140 MPa at 180 days. To achieve this a 0.24 water/cement ratio and 3.5% super plasticiser were used. The investigation used three levels of silicafume (0, 10%, 20% by weight of cement), two coarse aggregate proportions of total aggregate (0.48, 0.65 by volume) and both magnetite and natural sand fine aggregate were used. The effect of transient high temperature on strength of heavyweight high strength concrete was investigated. There were three exposure durations (0, 1hr, 2hrs.)at temperatures of 100, 300, 500 and 700 °C. As the temperature increased to 100 °C, the strength decreased compared to the room temperature strength. With further increase in temperature, the specimens recovered the strength loss and reached a peak strength of 10 to 30 % above the room temperature strength. At the temperature 500 and 700 °C, the strength in each case dropped sharply.

在目前的工作下,为实现坍落度大约为100毫米、在180天时抗压强度达到140 MPa以上，选择了12混合。为了实现这一目的，使用0.24的水灰比和3.5%超级增塑剂。调查使用了硅粉的三个等级(水泥重量的0、10%、20%),同时，也使用了总比例中的两个粗骨料比例(体积的0.48,0.65)，磁铁矿和天然砂细骨料。调查了瞬态高温对高强重混凝土强度的影响。在- 100、300、500和700°C的温度下，有三个持续的接触时间(0、1小时、2小时。)。当温度增加到100°C,与室温时的强度相比有所下降。随着温度的进一步提高,样本的强度损失有所恢复，并且达到峰值，为室温强度的10到30%。在500和700°C时,在不同情况下强度都急剧下降。

Keywords: heavyweight concrete, high strength concrete; magnetite concrete; heavyweight aggregate; high temperature; elevated temperature; compressive strength.

关键词：重混凝土，高强混凝土，磁铁矿混凝土，重骨料，高温，升温，抗压强度

INTRODUCTION

介绍

For shielding from gamma rays and X-rays the density of the concrete is the most important parameter and increasing the density leads to reduced thickness of concrete required. Thermal stresses are generated either by external sources of heat as, for example, in the case of shields for nuclear reactors, or from heat arising from the attenuation or absorption of gamma and neutron radiation within the shield. Davis (1) pointed out that in most shielding structures stresses due to thermal effects or thermal loads could be of greater importance than stresses due to mechanical or non-thermal loads on the structure.

为了屏蔽伽马射线和x射线，混凝土的密度是最重要的参数并且增加密度会导致所需的混凝土厚度的减少。温度应力的产生，要么是外部热源导致,例如,核反应堆的盾,要么是由盾内gamma;射线的衰减或吸收和中子辐射引起。Davis(1)指出,在大多数屏蔽结构中，由于热作用或热负荷导致的承重可能比由于机械结构或非热能的负载造成压力的承重更加重要。

Three types of tests are commonly used to study the effect of transient high temperature on

三种类型的测试通常用来研究瞬态高温的影响

1 Mansoura University, El-Mansoura, Egypt. E-mail: mmahdy@mum.mans.eun.eg

2 School of Engineering, City University, London, UK. E-mail: P.R.S.Speare@city.ac.uk

3 Dept. of Structural Eng., Mansoura University, El-Mansoura, Egypt.

1曼苏拉大学,El-Mansoura，埃及。电子邮件:mmahdy@mum.mans.eun.eg

2机械学院,城市大学,伦敦,英国。电子邮件:P.R.S.Speare@city.ac.uk

3结构电子新闻采集的深度，曼苏拉大学,El-Mansoura,埃及。

the stress strain properties of concrete under axial compression:

轴向压缩下混凝土的应力应变特性:

1- Unstressed tests, where the specimens are heated under no initial stress and loaded to failure at the desired elevated temperature.

1-无应力测试,在没有初始应力条件下加热标本并且在既定升温下加载到破坏。

2- Stressed tests, where a fraction of the ultimate compressive strength at room temperature is applied and sustained during heating and, when the target temperature is reached, the specimens are loaded to failure.

2-压力测试,室温下的样本，部分加热时持续应用极限抗压强度，当达到预定温度时，样本加载至破坏。

3- Residual unstressed tests, where the specimens are heated without any load, cooled down to room temperature and then loaded to failure.

3-剩余的无应力测试,在没有任何荷载下加热标本,冷却至室温,然后加载至破坏。

In general, the residual unstressed strength is lower than the unstressed strength (2, 3). As temperature is increased, normal strength concrete initially experiences a 10% loss in strength up to a temperature of 125 °C. This is followed by a gain of strength of as much as 15% of the room temperature strength, up to 250 °C. With further increase in temperature, the strength drops rather rapidly, falling to as little as 20 percent of the original strength at 700 °C (4, 5). The moisture content at the time of testing has a significant effect on the strength of concrete at elevated temperature. Tests on sealed and unsealed specimens have shown that higher strength is obtained if moisture is allowed to escape (6, 7).

一般而言,残余的无应力强度低于无应力的强度(2、3)。随着温度增加,普通强度混凝土最初经历一个温度升至125°C强度损失10%的过程。这个过程是紧随在温度到达250°C时获得的强度大约为室温强度的15%之后。随着温度的进一步提高,在700°C(4、5)时强度下降相当迅速，下降低到原始强度的20%。在升温时，测试含水率对混凝土的强度有显著的影响。测试密封和启封样本表明,如果允许释放水分会获得更高的强度(6、7)。

RESEARCH SIGNIFICANCE

研究意义

With increasing use of high strength concrete, the risk of exposure to high temperatures has also increased. To be able to assess the structural safety of such structures after exposure to high temperature, it is important that the effect on strength be well understood. This paper provides initial findings of an ongoing study on the behavior of heavy weight high strength concrete under extreme temperature conditions.

随着高强混凝土的使用增加,暴露在高温下的风险也增加了。为了能够评估这种暴露于高温后的结构的安全,更好地理解强度的影响是重要

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