1、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-HeatPortland Cement ConcreteAbstract: 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 an
2、d 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 1010-6-1510-6
3、 than 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 cement1 IntroductionThe investigation on crack of mass concrete is a hot problem to whic
4、h 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 concrete1-3. So the key technology on mass concrete is how to reduce thermal displacements and enhance the crack resistance of concrete.As we
5、ll known, the hydration heat of bonding materials is the main reason that results in the temperature difference between outside and inside of mass concrete4,5. In order to reduce the inner temperature of hydroelectric concrete, several methods have been proposed in mix proportion design. These inclu
6、de 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, etc6,7. So it is more reasonable to use MHC in application of mass concrete.Low-heat portl
7、and 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 excelle
8、nt durability, etc, so the further study continues to be important8-10. The long-term strength of C2S can approach to or even exceed that of C3S11. In addition, C2S has a series of characteristics superior to C3S. These include the low content of CaO, low hydration heat, good toughness, compact hydr
9、ation products, excellent resistances to chemical corrosion, little dry shrinkage, etc12,13.For hydroelectric concrete , the design requirements have some characteristics, such as long design age, low design strength, low hydration temperature rise, and low temperature gradient14. All these requirem
10、ents 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
11、the moderate-heat Portland cement (MHC) concrete, the anti-crack behavior of LHC concrete was analyzed.2 ExperimentalMHC 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 compositio
12、ns 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 diff
13、erent 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 t
14、han 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 c
15、oncrete 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
16、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
17、-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
18、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, al
19、l 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
20、 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 exci
21、ter 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 DiscussionIn this experiment, ZB-1A type retarding superplasticizer and DH9 air-entraining agent were used. The dosage of ZB-1 was 0.
22、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
23、: 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
24、% 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 propertiesThe physical and mechanical properties include strength, elastic modulus, limits tension, and so on.
25、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 M
26、HC 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 2
27、8.3 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 fl
28、y 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
29、 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 1010-6 t
30、o 15 10-6 than that of MHC, and the 90-day limits tension of LHC concrete is increased by 1210-6 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 concret
31、e.3.2 Deformation characteristicsDeformation 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 low
32、er 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 40810-6. As a result, the volume stability of LHC concrete is better than that of MHC concrete i
33、n 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
