举例英文原文及翻译适用于毕业论文引用文献.doc

建筑工程 英文原文及翻译
Effect of Water Content on the Properties of Lightweight Alkali-Activated Slag Concrete
Keun-Hyeok Yang，Ju-Hyun Mun，Jae-Il Simand Jin-Kyu Song
Keyword：concrete、water content
Introduction
With the gradual growth of a global effort to reduce greenhouse gas emissions, a large section of the concrete industry has growing interest in minimizing the use of ordinary portland cement (OPC). This is because it is estimated that the production of 1 t of OPC requires about 2.8 t of raw materials, such as limestone and coal, and releases about 0.7 t of carbon dioxide (CO2) to the earth’s atmosphere from the decarbonation of lime in the kiln (Gartner 20046). As a result, since the late 1980s, toward the reduction of the use of OPC, various investigations have been conducted in several fields to develop a cementless alkali-activated (AA) ground granulated blast furnace slag binder together with a fly ash–based geopolymer binder. As pointed out by Shi et al. (200611), AA slag binders and concrete will gradually attract a great deal of interest because of their extensive advantages of lower carbon emissions and energy cost, higher-strength development, and better durability than with OPC concrete. In particular, AA slag concrete can effectively be applied to precast concrete products.
It is generally estimated that the amount of CO2 emitted from the consumption of fossil fuels for commercial and residential heating accounts for approximately 12% of the total CO2 emissions into the earth’s atmosphere. In addition, the nonnegligible amounts of CO2 are emitted from buildings or factory cooling. As a result, the development of energy saving systems and new and renewable energy sources has become one of the hottest issues in building structures. The use of lightweight concrete as a building material is highly effective for saving energy because of the enhanced thermal insulation capacity through the lower thermal conductivity of lightweight aggregates. In addition, the application of structural lightweight concrete has several advantages as the reduction of the dead load because a lower density of concrete allows for smaller and lighter weight structural member that can lead to more available space and improves the seismic resistance capacity of the upper structures. Furthermore, the smaller and lighter elements of precast concrete members are preferred to make the handling and transporting system less expensive.
Synergy effects are expected when AA slag binder and lightweight aggregates are combined to produce environmentally friendly concrete because of the various advantages of both materials. One of the most significant effects is the highly reduced CO2 emission from concrete building structures by the use of AA slag binder with a lower CO2 emission and an energy-saving effect owing to the use of lightweight aggregates. In addition, precast concrete can be produced with good quality and economical efficiency from an early higher strength development capacity of AA slag paste and a lower density of aggregates. However, the available experimental data (Collins and Sanjayan 19995; Yang et al. 200917) needed to determine a reliable mixing design and the mechanical properties of lightweight AA slag concrete are very rare. Unlike normal-weight OPC concrete, the workability and development of compressive strength of lightweight AA slag concrete is very sensitive to the hydration rate of the binder, the physical properties of lightweight aggregates, and the mixing conditions, such as the water content, water-binder ratio, and the proportion of lightweight aggregates. Yang et al. (200917) showed that the initial slump and the slump loss of AA slag concrete are significantly affected by the water-binder ratio and lightweight aggregate proportions caused by the high water absorption capacity of lightweight aggregates. Collins and Sanjayan (19995) also pointed out that the internal curing effect on the slump loss and the shrinkage of concrete is strongly dependent on the state of moisture in lightweight aggregates and water content. In addition, a quicker slump loss is generally observed in lean AA slag concrete mixes than in OPC concrete because of the fast chemical reaction between various alumino-silicate oxides with silicate and/or the formation of silica-rich calcium silicate hydrates gel (Shi et al. 200611). Therefore, the water content and lightweight aggregate proportions need to be significantly managed for realizing the targeted slump and retarding the slump loss of lightweight AA slag concrete.
In the present study, five all-lightweight and five sand-lightweight AA slag concrete mixes were tested to evaluate the effect of the water content on the workability, mechanical properties, and shrinkage strain of the concrete. The rate of compressive strength development and the shrinkage strain were measured and compared with the empirical models proposed by American Concrete Institute (ACI) 209 (ACI 19941) for normal-weight portland cement concrete. To examine the practical applicability of the lightweight AA slag concrete, the splitting tensile strength and the moduli of elasticity and rupture recorded from the concrete specimens were compared with the values predicted through various sources for lightweight OPC concrete, whenever possible. These sources included design equations specified in ACI 318-08 or Eurocode 2 [British Standards Institution empirical equations proposed by Slate et al., and a database compiled by Sim and Yang.
Experimental Details
Materials
Ground granulated blast furnace slag (GGBS) was activated by sodium silicate (Na2O·SiO2) and calcium hydroxide [Ca(OH)2] powders and used as a cementitious binder. The GGBS used for the source material had a high CaO content and SiO2-to-Al2O3 ratio by mass of 2.29. The specific gravity and specific surface area measured for the GGBS were 2.2 and 4,200  cm2/g, respectively. The sodium silicate powder used was a compound of 50.2% sodium oxide (Na2O) and 45% silicon oxide (SiO2), producing a molar ratio (SiO2/Na2O) of 0.9. The purity of the Ca(OH)2 powder used was 95.8%.
Wang et al. showed that a higher strength of AA GGBS concrete was obtained by using liquid sodium silicate with a molar ratio of 1 to 1.5. Yang et al. (200816, 201015) also recommended that the ratios by weight of Ca(OH)2 to the binder, including the GGBS and alkali activators, and of Na2O in sodium silicate to GGBS were above 7.5% and 3%, respectively, to facilitate the chemical reaction by ion exchange between the silicate anions of the GGBS and the cations of the alkaline activators. Therefore, the Ca(OH)2-to-binder ratio was selected to be 7.5% and sodium silicate was added so that the Na2O-to-GGBS ratio would be 3% to produce a cementless AA slag binder.
Artificially expanded clay granules with maximum sizes of 19 mm and 5 mm were used for lightweight coarse and fine aggregates, respectively. Locally available natural sand with a maximum particle size of 5 mm was also used for normal-weight fine aggregates. From X-ray diffraction measurements, the main composition of the lightweight aggregates was quartz and calcium aluminum silicate. Fig. 1 shows that the lightweight aggregates were spherical in the shape and had a closed surface with a slightly rough texture. The core of the particle had a uniformly fine and porous structure that led to high thermal and acoustic insulation but induced high water absorption and low strength. In particular, the rate of water absorption of lightweight aggregates was extremely fast for the lightweight aggregates during the first 3 h, and then the absorption rate slowed down, as shown in Fig. 2. The specific gravity of the lightweight aggregates used was approximately 2.5 times lower than that of natural sand. The particle distribution of lightweight aggregates showed a continuous grading that satisfied the standard distribution curves recommended in the Korea Industrial Standard (Korean Standards Information Center 20068) specification, as plotted in
Fig 1.
Shape and scanning electron microscope (SEM) images of the lightweight coarse aggregate used

Fig 2.
Water absorption rates of the aggregates used

Fig 3.
Particle distribution curves of the aggregates used: (a) lightweight aggregates; (b) normal-weight aggregates (natural sand)

Mix Proportions
Five all-lightweight and five sand-lightweight AA slag concrete mixes were prepared by varying the water content per unit volume of concrete, as given in Table 2. Higher water-binder ratios can result in segregation in the lightweight concrete (ACI 19982). In addition, the compressive strength of lightweight AA slag concrete targeted in the present study was above 24 MPa for application to structural concrete members. From various preliminary tests, the water-binder ratio by weight and fine aggregate-to-total aggregate ratio by volume were fixed at 30% and 40%, respectively, in all concrete mixes. The mixture proportions of all the concrete specimens were determined on the basis of the weight method proposed by ACI 211.
Mixing, Curing, and Testing
Lightweight aggregates and natural sand were dampened for 24 h and then air-dried for another 24 h to simulate the saturated surface dried-state that is commonly employed in ready-mixed concrete plants. The alkaline binder and aggregates were dry-mixed in a pan mixer for 1 min, then water was added and mixed for another 1 min. For all the concrete mixes, a polycarbonate-based water-reducing admixture with an air-entraining agent was added by 0.5% relative to the amount of binder used. After the initial slump was tested, each mix was poured into various steel molds to measure the compressive strengths and other mechanical properties. Immediately after casting, all specimens were cured at room temperature until testing at the specified ages.
Test Results and Discussions
Initial Slump and Slump Loss
The initial slump, Si, of the lightweight AA slag concrete increased with the increase of water content, which is generally observed in the lightweight OPC concrete as well (Neville 19959). At the same water content, the all-lightweight AA slag concrete showed a higher value of initial slump than the sand-lightweight AA slag concrete, as shown in Table 3. The relatively round and smooth surface texture of the lightweight aggregates led to the improved initial workability of concrete.
The slump, S, of the concrete tested sharply decreased over the elapsed time, indicating that a more notable slump loss developed in all-lightweight AA slag concrete than in sand-lightweight AA slag concrete, as shown in Fig. 2, and the rapid reaction of sodium silicate resulted in the quick setting of concrete. However, the increase of water content alleviated the slump loss of the concrete specimens. This may be attributed to the increased water content resulted in a decrease in the volume of lightweight aggregates mixed in the concrete and an increase of the free water between hydrated gels., the relative slump, S/Si, of lightweight AA slag concrete can be approximately expressed as kT+1 with respect to the elapsed time, whereas S is slump at a specified time after the concentration and kind of alkali activator have an effect on the slump loss of concrete, this is seldom evaluated quantitatively, as reliable test data are very rare. Therefore, based on a nonlinear multiple regression analysis considering the effect of only the volumes of the water content, Wv, and the lightweight aggregates, Lav, the rate of the slump loss, k, of lightweight slag concrete activated by Ca(OH)2 and Na2O·SiO2 can be expressed in the following form, as presented in Fig. 5:

Fig 4.
Relative slump against the elapsed time: (a) all-lightweight concrete; (b) sand-lightweight concrete

Fig 5.
Effect of the volumes of water and lightweight aggregates on the rate of slump loss
The failure planes of lightweight concrete generally pass through the lightweight aggregates and the number of interfacial cracks between lightweight aggregates and pastes increases with the increase in the amount of lightweight aggregates . As a result, the reduced volume of lightweight aggregates mixed in the concrete because of the increased water content can lead to a slightly higher compressive strength of concrete. Additionally, the compressive strength of lightweight concrete increased with the increase of its dry density, showing a similar increasing rate in both lightweight AA slag and OPC concretes, as presented in Fig. 6. At the same dry density, a higher strength was observed in lightweight AA slag concrete than in lightweight OPC concrete. It is generally known that the sodium-containing hydrated gels formed in AA slag pastes have low and tighter intensities than those generally observed in OPC pastes. This more elaborated gel product reduces interfacial cracks between lightweight aggregates and pastes, which can lead to an increase of compressive strength of concrete.

Fig 6.
Dry density versus 28-day compressive strength
In general, the development of the compressive strength of OPC concrete is simulated as a parabolic function, as the increasing rate of compressive strength development decreases with the increase of age. The ACI 209 (ACI 19941) proposed the compressive strength development of cement concrete with age in the following form:

where fc′(t) = compressive strength at age t (in days). The constants A1 and B1 in Eq. (2) generally relate to the development of strength at an early age and a long-term age, respectively. In particular, lower values of A1 and B1 indicate higher rates of compressive strength development at the early and long-term ages, respectively. The compressive strength development of concrete tested occurred in a parabolic shape, as shown in Fig. 7. From the test results given in Table 3, the constants A1 and B1 in Eq. (2) were determined from nonlinear regression analysis using the SPSS software, whereby a correlation coefficient above 0.96 was obtained for all the concrete specimens.

Fig 7.
Typical compressive strength development of all-lightweight AA slag concrete
The constants A1 and B1 determined from the concrete tested are plotted in Fig. 8. In the same figure, both constants specified in ACI 209 (ACI 19941) for cement concrete are also given for comparisons. The strength gain of lightweight AA slag concrete at an early age was highly rapid, indicating that the compressive strength at 1 day reached as high as above 75% of the 28-day compressive strength. As a result, the constant A1 for lightweight AA slag concrete was lower than that for OPC concrete and even that for high early strength portland cement concrete cured under steam, as shown in Fig. 8.

Fig 8.
Comparisons of both constants in Eq. (2) determined from concrete specimens and specified in ACI 209 (ACI 19941)
Splitting Tensile Strength
The normalized splitting