外文翻译--低热硅酸盐水泥混凝土的抗裂性能

外文翻译
Anti-Crack Performance of Low-Heat
Portland Cement Concrete
Abstract: The properties of low-heat Portland cement concrete(LHC) were studied in detail. The experimental results show that the LHC concrete has characteristics of a higher physical mechanical behavior, deformation and durability. Compared with moderate-heat Portland cement(MHC), the average hydration heat of LHC concrete is reduced by about 17.5%. Under same mixing proportion, the adiabatic temperature rise of LHC concrete was reduced by 2 ℃-3℃,and the limits tension of LHC concrete was increased by 10×10-6-15×10-6than that of MHC. Moreover, it is indicated that LHC concrete has a better anti-crack behavior than MHC concrete. Key words: low-heat portland cement; mass concrete; high crack resistance; moderate-heat portland cement
1 Introduction
The investigation on crack of mass concrete is a hot problem to which attention has been paid for a long time. The cracks of the concrete are formed by multi-factors, but they are mainly caused by thermal displacements in mass concrete[1-3]. So the key technology on mass concrete is how to reduce thermal displacements and enhance the crack resistance of concrete.
As well known, the hydration heat of bonding materials is the main reason that results in the temperature difference between outside and inside of mass concrete[4,5]. In order to reduce the inner temperature of hydroelectric concrete, several methods have been proposed in mix proportion design. These include using moderate-heat portland cement (MHC), reducing the content of cement, and increasing the Portland cement (OPC), MHC has advantages such as low heat of hydration, high growth rate of long-term strength, etc[6,7]. So it is more reasonable to use MHC in application of mass concrete.
Low-heat portland cement (LHC), namely highbelite cement is currently attracting a great deal of interest worldwide. This is largely due to its lower energy consumption and CO2 emission in manufacture than conventional Portland cements.
LHC has a lot of noticeable properties, such as low heat of hydration excellent durability, etc, so the further study continues to be important[8-10]. The long-term strength of C2S can approach to or even exceed that of C3S[11]. In addition, C2S has a series of characteristics superior to C3S. These include the low content of CaO, low hydration heat, good toughness, compact hydration products, excellent resistances to chemical corrosion, little dry shrinkage, etc[12,13].
For hydroelectric concrete , the design requirements have some characteristics, such as long design age, low design strength, low hydration temperature rise, and low temperature gradient[14]. All these requirements agree with the characteristics of LHC. Furthermore, LHC has a high hydration activity at later ages, the effect of which can improve the inner micro-crack. Based on above-mentioned analyses, the properties of low-heat Portland cement concrete were studied in detail in this paper. Compared with the moderate-heat Portland cement (MHC) concrete, the anti-crack behavior of LHC concrete was analyzed.
2 Experimental
MHC was produced in Gezhouba Holding Company Cement Plant, China; and LHC was produced in Hunan Shimen Special Cement Co. Ltd., China. The chemical compositions and mineral compositions of cement are listed in Table 1 and Table 2 respectively, and the physical and mechanical properties of cement are listed in Table 3.
In spite of a little difference in chemical compositions, there is an obvious dissimilarity between the mineral component of LHC and that of MHC because of the different burning schedule. The C3S (Alite) content of MHC is higher than that of LHC, and the C2S (Belite) content of LHC is higher than that of MHC. Alite is formed at temperatures of about 1 450 ℃, while Belite is formed at around 1 200 ℃. Therefore, LHC can be manufactured at lower kiln temperatures than MHC. And the amount of energy theoretically required to manufacture LHC is lower than that of MHC.
Belite hydrates comparatively slowly, and the early compressive strengths of pastes, mortars, and concretes containing LHC are generally lower as a result. The long-term strength and durability of concrete made from LHC can potentially exceed those of MHC. The results from Table 3 show that the early strength of LHC pastes is lower than that of MHC pastes, and that the strength growth rate of LHC is higher than that of MHC.
The hydration heat of bonding materials was tested. Class I fly ash of bonding materials came from Shandong Zhouxian Power Plant, China. The experimental results shown in Table 4 indicate that the hydration heat of LHC is much lower than that of MHC. The 1-day, 3-day and 7-day hydration heat of LHC without fly ash is 143 kJ/kg, 205 kJ/kg, 227 kJ/kg, respectively. The 1-day, 3-day and 7-day hydration heat of MHC without fly ash is 179 kJ/kg, 239 kJ/kg, 278 kJ/kg, respectively. Compared with MHC, the average hydration heat of LHC concrete is reduced by about 17.5%. Obviously, low hydration is of advantage to abate the pressure to temperature control, and to reduce the crack probability due to the temperature gradients. The adiabatic temperature of LHC concrete and MHC concrete was tested. As a result, the adiabatic temperature rise of LHC concrete is lower than that of MHC concrete and the different value ranges from 2 ℃to 3 ℃in general.
After adding fly ash, all specimens show a lower hydration heat, and it decreases with increasing fly ash content. For MHC with 30% fly ash, the 1 d, 3 d, 7d accumulative hydration heat is reduced by 14.5%, 20.5%, 21.9%, respectively; and for LHC with 30% fly ash, the 1 d, 3 d, 7 d accumulative hydration heat is reduced by 21.7%, 26.3%, 23.3%, respectively. Obviously, the effect of fly ash on the hydration heat of LHC is more than that of MHC. It is well known that the fly ash activation could be activated by Ca(OH)2. LHC has a lower content of C3S and a higher content of C2S than MHC, so the Ca(OH)2, namely the exciter content in hydration products of LHC pastes is lower. Decreasing the hydration activation of fly ash reduces the hydration heat of bonding materials.
3 Results and Discussion
In this experiment, ZB-1A type retarding superplasticizer and DH9 air-entraining agent were used. The dosage of ZB-1 was 0.7% by the weight of the blending, and the dosage of DH9 was adjusted to give an air-containing of 4.5% to 6.0%. The parameters that affected the dosage included the composition and the fineness of the
cement used, and whether the fly ash was used. Four gradations of aggregate were used, 120 mm-80 mm: 80 mm-40 mm: 40 mm-20 mm: 20 mm-5 mm=30:30:20:20.
The term water-to-cementitious was used instead of water-to-cement, and the water-to-cementitious ratio was maintained at 0.50 for all the blending. The slump of concrete was maintained at about 40 mm, and the air content was maintained at about 5.0% in the experimental. After being demoulded, all the specimens were in a standard curing chamber. The mix proportion parameter of concrete is listed in Table 5.
3.1 Physical and mechanical properties
The physical and mechanical properties include strength, elastic modulus, limits tension, and so on. The results of strength shown in Table 6 indicate the early strength (7 d curing ages) of LHC (odd samples) concrete increases slowly. The ratio between 7 d compressive strength and 28 d compressive strength of LHC concrete is about 0.4, while for MHC concrete the ratio is about 0.6. Compared with MHC concrete, the growth rate of strength of LHC concrete becomes faster after 7 d curing ages. The compressive strength for 28 d, 90 d, 180 d curing ages of LHC concrete containing 20% of fly ash is 30.2 MPa, 43.8 MPa, 48.5 MPa, respectively, while that of MHC concrete containing 20% of fly ash is 28.3 MPa, 35.6 MPa, 39.8 MPa, respectively. The content of C2S in LHC is higher than that in MHC, which results in the above-mentioned difference.
Table 6 shows that the strength growth rate of concrete made with fly ash blended cements is higher than that of blank specimens; the more the dosage of fly ash, the higher the growth rate. Fly ash has a glassy nature, which can react with Ca(OH)2. Since Ca(OH)2 is a hydration product of cement, the reaction between fly ash and Ca(OH)2, called “secondary hydration”, will happen at latish ages. The magnitude of Ca(OH)2 is affected by some factors, such as the water-to-cementitious,
the dosage of cement.
The elastic modulus and the limits tension of concrete are given in Table 7. Under same mixing proportion, the elastic modulus of LHC concrete is approximately equal to that of MHC; the 28-day limits tension of LHC concrete is increased by 10×10-6 to 15 ×10-6 than that of MHC, and the 90-day limits tension of LHC concrete is increased by 12×10-6 than that of MHC concrete. The above results show that the use of LHC improves the limits tension of concrete. Increasing the limits tension of concrete will be benefit to the crack resistance of concrete.
3.2 Deformation characteristics
Deformation characteristics of concrete include drying shrinkage, autogenous deformation, creep, etc. The drying shrinkage of concrete is shown in Fig.1. The drying shrinkage increases with age. At early ages a up to 90 days, all the LHC
concrete specimens show a lower drying shrinkage; and it decreases with increasing the fly ash content. When containing 30% of fly ash, the drying shrinkage of LHC concrete is 363 ×10-6 at 90 days, while for MHC concrete the value is 408×10-6. As a result, the volume stability of LHC concrete is better than that of MHC concrete in drying environment.
Experiment results of autogenous deformation of concrete are given in Fig.2. There is an obvious difference between the development of autogenous deformation of LHC concrete and that of MHC concrete. The autogenous deformation of LHC concrete has an expansive tendency. At early ages up to 14 days, the autogenous deformation of pure LHC samples increases with age, and the 14-day value reaches a peak of 20×10-6. The autogenous deformation of pure LHC samples decreases with age at 14 days to 90 days, and the 90-day value is 10×10-6. After adding 30% of fly ash, the autogenous deformation of LHC concrete increases with age, and the 90-day value is 61×10-6. The autogenous deformation of MHC concrete has a tendency to shrink, especially without fly ash.
3.3. Durability
The durability of concrete is evaluated by antipenetrability grade and frost-resistant level. Under the pressure of 1.2 MPa, the permeability height of pure LHC samples is 3.1 cm, while that of pure MHC samples is 2.0 cm. The test data
indicate that the LHC concrete has an excellent performance in anti-penetrability, as well as MHC concrete. The permeability of concrete increases somewhat with addition of fly ash. At the end of the 250 freezing and thawing cycling, there is a little difference in both mass and resonant frequency. Both LHC concrete and MHC concrete show an excellent frost-resistant behavior. The results of this work confirm that LHC concrete systems have an adequate anti-penetrability and frost-resistance to adapting design requirement.
3.4 Analysis of crack resistance
In order to control the crack phenomena, it is important to accurately evaluate the anti-crack behavior.
As well known, concrete is a kind of typical brittle materials, and its brittleness is associated with the anti-crack behavior[15]. The brittleness is measured by the ratio of tension strength to compressive strength. With the increase of the ratio, concrete has a less brittleness, better crack resistance and toughness. It is indicated from the experiment results shown in Table 6 that the ratio of LHC concrete at all stages of hydration is higher than that of MHC concrete, which shows that LHC concrete has a better anti-crack behavior.
In the crack control and design of hydroelectric mass concrete, the original evaluation of crack resistance behavior of concrete is using the utmost tensile strength which is shown in the following expression of Eq.1.
σ=εP E (1)
where, εP is the limits tension of concrete, and E is the elastic modulus of tension, which is assumed to be equal to the elastic modulus of compression[16].
It is indicated from the calculation results shown in Table 8 that the utmost tensile strength of LHC concrete at all stages of hydration is higher than that of MHC cncrete.
The research on materials crack resistance which is the basis for esign, construction and the choice of raw materials, has been popular in today’s world. Through a great deal of research, it is widely thought that concrete with a better crack resistance has a higher tension strength and limits tension, lower elastic odulus and adiabatic temperature rise and better volume stability[17,18].
Based on above-mentioned results, the LHC concrete has a higher tension strength and limits tension, lower elastic modulus and adiabatic temperature rise, and lower drying shrinkage than MHC concrete. Compared with MHC concrete, the autogenous deformation of LHC concrete has an expansive tendency. Although the early strength of LHC concrete is lower than that of MHC concrete, its later strength has approached to or even exceed that of MHC concrete.
4 Conclusions
a) The early compressive strength (7 d curing ages) of LHC is lower, but its later strength (28 d, 90 d curing ages) has approached to or even exceed that of MHC.
b) Compared with MHC, the average hydration heat of LHC concrete is reduced by about 17.5%.
c) Under the same mixing proportion, the elastic modulus of LHC concrete is approximately equal to that of MHC, and the limits tension of LHC concrete is increased by 10×10-6-15×10-6 than that of MHC.
d) The drying shrinkage of LHC concrete is obviously smaller than that of MHC concrete, and the autogenous deformation of LHC concrete has a tendency to expand.
e ) The LHC concrete has a better anti-penetrability and frost resistance, as well as the MHC concrete.
f) At all stages of hydration, the anti-crack strength of LHC concrete is higher than that of MHC concrete, and the former has a higher ratio of tension strength to compressive strength.
References
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低热硅酸盐水泥混凝土的抗裂性能
摘要：低热硅酸盐水泥混凝土（LHC）的特性详细地被研究。

实验的结果表示LHC 混凝土有比较高实际的机械行为、形变和耐久性的特性。

与中热硅酸盐水泥（MHC）相较, LHC 混凝土的平均水合作用热被减少大约17.5%.在相同的混台比例比率之下，LHC 混凝土的断热温升减少了 2 ℃-3℃，而且LHC 混凝土的限度张力比MHC 增加了10 ×10-6-15 ×10-6。

而且，它表明LHC 混凝土比MHC 有更好的反裂痕行为。

关键词: 低热硅酸盐水泥; 大体积混凝土; 高抗裂; 中热硅酸盐水泥
1、介绍
调查在大体积混凝土的裂纹是一个热门问题，已将注意了很长一段时间。

混凝土的裂痕有多的因数造成的，但是他们主要地由大众的混凝土中的热的位移所引起［1-3]。

因此在大众的混凝土上的主要的技术是该如何减少热的位移而且提高混凝土的反裂痕能力。

众所周知，粘结材料的水化作用热是造成大众混凝土外部和的内部之间温差的主要原因［4,5]。

为了要减低水化作用混凝土的内部温度，一些方法已经在混合比例比率设计方案中被提出。

这些包括使用中热硅酸盐水泥(MHC)，减少水泥的用量，增加普通硅酸盐水泥(OPC)，MHC有好处例如低水化热，长期强度的高增长率[6，7]。

因此在大众混凝土使用中用MHC更合理。

低热硅酸盐水泥（LHC）, 即高硅水泥现在正在吸引全世界很多人的兴趣。

这主要是由于它在制造过程中比传统的硅酸盐水泥消耗较低的能量和排放更少的CO2。

LHC 有许多引人注目的特性，像是水合作用是放热少、优良耐久性，及其他，因此持续更高深的研究是很重要的［8-10] 。

C2S 的长期强度能接近或者超过C3S的长期强度［11] 。

此外，C2S有一系列的特征优于C3S。

这些包括更少的游离CaO，低水化热，良好的韧性，坚固的水化产物，良好的防化学腐蚀性，良好的安定性，等等［12-13]。

因为水化混凝土，设计需要有一些特性，像是长设计材龄，低设计强度、低水合作用温升和低的温度梯度［14]。

这些需要符合LHC 的特性。

此外，LHC 在后期有一个高水合作用，水化作用能改良材料内部微裂纹。

综上所述，低热硅酸盐水泥混凝土的特性在文中详细地研究。

与中硅酸盐水泥（MHC）混凝土相比，LHC混凝土的反裂痕行为被分析了。

2 实验
MHC 在中国葛洲坝股份公司水泥厂生产；LHC 在中国湖南石门特殊水泥公司生产。

水泥的化学成分和矿物合成在表1和表2 分别地列出来，水泥的物质和机械，虽然化学成分差别不大，但在不同的燃烧条件下MHC 和LHC 的矿物组成却明显不同。

MHC的C3S（Alite）含量比LHC高，但是LHC的C2S（Belite）含量比MHC 高。

Alite 在温度大约1450℃形成, 当Belite 在1200℃左右时形成. 因此，LHC能在比MHC更低的窑炉温度下被烧成。

而且理论上LHC烧成时比MHC节省更多的能量。

Belite水化反应时放热相对比较慢，所以导致含有LHC 的浆体、耐火水泥
和混凝土的早期抗压强度通常比较低。

以LHC为原料的混凝土的长期强度和耐久性可能超过MHC。

表 3 的结果显示LHC浆体的早期强度比MHC低，但是LHC 的强度增长率比MHC高。

会黏结材料的水合作用热测试。

第一阶段黏结材料的粉煤灰来自中国山东周县发电厂。

表4显示的实验的结果表明LHC 的水合作用热比MHC低很多。

没有粉煤灰的LHC的1天、3天和7天的水合作用热分别是143 kJ/kg、205 kJ／kg，227 kJ／kg。

没有粉煤灰的MHC的1天、3天和7天的水合作用热分别是179 kJ/kg、239 kJ／kg，278 kJ／kg。

LHC 混凝土的平均水合作用热比MHC减少了大约17.5%.显然地，低的水合作用对温度控制降低压力有利，降低由于温度梯度引起的裂纹。

LHC混凝土和MHC混凝土的绝热温度测试。

结果，LHC 混凝土的绝热温升比MHC 混凝土低2 ℃--3 ℃。

在添加粉煤灰之后，所有试样都表有一个更低的水合作用热，而且它随着粉煤灰含量减少而增加。

对于MHC用30%粉煤灰，1天、3天，7 天总的水合作用热分别减少了14.5%、20.5%、21.9%；而对于LHC用30%的粉煤灰1天、3天、7天总的水合作用热分别减少了21.7% 、26.3%、23.3%。

明显，粉煤灰的影响在LHC的水化热多过MHC。

众所周知，Ca（OH）2能激活粉煤灰的活性。

LHC比MHC有更少的C3S更多的C2S，因此Ca（OH）2, 即LHC浆体的在水合作用的产物激发物含量下降。

随着粉煤灰的水合作用活化的减少减少黏结材料的水合作用热也随之减少。

3、结果与讨论
在这实验中，用ZB-1 A型态妨碍超塑性和DH9外加剂。

ZB-1 的药量是混合的重量的0.7% ，而且DH9 的药量被调整呆了外加剂的 4.5%-6.0%。

不管粉煤灰是否被用，影响了药量的参数的事的水泥合成物和水泥细度。

凝聚体的四个阶度是120毫米－80毫米：80毫米－40毫米：40毫米－20毫米：20毫米－5毫米＝30:30:20:20。

在水－类水泥代替用了水－水泥期间，水－类水泥在所有的混合物中的比率维持在0.50。

在试验中，混凝土的大裂纹被控制在大约40 毫米之内，空气含量被控制在大约5.0%。

在被脱模后，所有样本放在一个标准养护室中养护。

混凝土的混合比例比率参数在表 5 被列出来了。

3.1 物理力学性能
物理力学性能包含强度、硬度、屈服强度等等。

表6显示LHC（单数的样本）的早期强度（7 d 强度）是缓慢增长的。

LHC混凝土的7 d抗压强度和28d 抗压强度之间的比例大约0.4 ，而MHC混凝土的比例大约是0.6。

与MHC混凝土相比较，LHC混凝土强度的增长率在7 d之后增长得更快。

含20%粉煤灰的LHC混凝土在28 d 、90 d、180 d后的抗压强度分别是30.2 MPa、43.8 MPa、48.5 MPa，含20%粉煤灰的MHC混凝土在28 d 、90 d、180 d后的抗压强度分别是28.3 MPa、35.6 MPa、39.8MPa。

造成上述差异的原因是LHC的C2S含量比MHC高。

表6表示与参入粉煤灰的水泥的强度增长率比不加的的高；粉煤灰的添加量愈多，增长率也愈高。

粉煤灰有玻璃的性质，可以与Ca（OH）2反应。

因为Ca （OH）2是水泥的水水化产物，粉煤灰和Ca（OH）2之间的反应,被称为“第二水化反应”，将在迟些时候发生。

Ca（OH）2的多少被一些因数影响，比如水浆体，水泥的添加量。

在表7中给模量和屈服极限。

在相同的混合比例下，LHC 混凝土的弹性模量和MHC大约相等；LHC 混凝土的28 天的屈服极限比MHC增长了10×10-6-15×10-6，而LHC混凝土的90天的屈服极限超过了MHC 混凝土12×10-6。

上述的结果表明LHC 的使用改良了混凝土的屈服极限。

增加混凝土的屈服极限将会
有利于混凝土的裂痕的出现。

3.2 形变特征
混凝土的形变特性含干燥收缩、自生的形变、潜动等等。

Fig.1显示了混凝土的干燥收缩。

干燥收缩是随时间增加的。

在刚到90天时，所有的LHC 混凝土试样表示一个低的干燥收缩；而且它随着粉煤灰的增加而降低。

当粉煤灰的含量为30%是，LHC混凝土在90天的干燥收缩为363×10-6，而为MHC混凝土数值是408×10-6。

结果，LHC 混凝土的安定性在干燥环境中比MHC 混凝土好。

Fig.2指出了混凝土的自生形变的实验结果。

MHC混凝土和LHC混凝土的自生形变的发展有明显不同。

LHC混凝土的自生形变有膨胀的趋向。

在刚到14天之前，纯LHC 样本的自生形变随时间增长，14天时达到最大20×10-6。

纯LHC 样本在14天至90天之间自生形变开始降低，在90 天的数值是10×10-6。

在添加30%的粉煤灰之后，LHC 混凝土的自生形变随时间增长，90天的数值是61×10-6 。

MHC 混凝土的自生形变有收缩的趋向，尤其是没有粉煤灰时。

3.3 耐久性
混凝土的耐久性是由防渗等级和抗冻性的水平决定的。

在1.2 MPa 的压力之下，纯的LHC样本的渗透的高度是 3.1 cm，而那纯MHC 样本是2.0 cm。

测试数据显示LHC混凝土在防渗透性方面比MHC 混凝土优秀。

混凝土的渗透性有时随着粉煤灰的增加而增长。

在250冻结要熔化快要结束的时候，质量和谐振频率中有一个小差异。

LHC混凝土比MHC混凝土有更好的抗冻性。

3.4 抗裂的分析
为了控制裂痕现象的出现，正确地评估反裂痕行为是很重要的。

恐怕最好知道，混凝土是一种典型的易碎材料，而且它的脆性与反裂痕行为有关[15]。

脆性对抗压和抗拉强度的比例是重要的。

随着比例的增大，混凝土的抗脆性比抗裂纹性和韧性更好。

表6的实验结果显示，LHC混凝土的比率在水合作用的所有级比MHC混凝土有比较好的反裂痕。

在裂缝控制和设计水力发电的大规模混凝土中，混凝土的反裂痕的最初评价正使用在的极度的抗拉强度用表达式Eq.1。

σ=ε PE
εP是混凝土的限度张力，E 是张力的弹性模量，假定和压缩的弹性模量相等[16]。

从计算结果表8上可以看出LHC的极度抗拉强度在水合作用的所有级中MHC混凝土高。

关于材料的抗裂纹的研究上是以智能卡、建筑和生料的选择为基础的，已经
流行于当今世界了。

通过大量的调查研究，人们广泛认识到混凝土有更好的抗裂纹能力、更高的抗拉强度好极限拉力，更低的弹性形变和隔热效果、更好的安定性[17,18]。

综上所述，HC混凝土有一个较高的拉力强度和极限拉，比较低的弹性模量和隔热效果，较低的干燥收缩比MHC混凝土。

与MHC混凝土相比，LHC混凝土的自生形变有易膨胀的趋向。

虽然LHC 混凝土的早期强度比MHC混凝土低，但他的它的后期强度接近或超过MHC混凝土。

4 结论
a) LHC 的早期抗压强度（7 d）比较低，但是它的后期强度（28 d，90 d）接近到或者甚至超过MHC。

b) 与MHC 相比，LHC 混凝土的平均水合作用热减少了大约17.5%。

c) 在一样的混合比例比例下，LHC 混凝土的弹性模量和MHC大致相等，LHC混凝土的极限拉力超过MHC混凝土10×10-6-15×10-6。

d) LHC 混凝土的干燥收缩明显比MHC 混凝土小，而LHC混凝土的自生形变有扩大的趋向。

e )LHC混凝土比MHC的抗渗性和抗冻性都要好。

f)在所有的水合作用中，LHC混凝土的反裂痕强度比MHC混凝土高，前者有一个更高的比例对与抗压强度和张力强度。

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