材料類外文翻譯---含氣量對輕質(zhì)混凝土滲透性的影響（英文）

1、The effects of air content on permeability of lightweight concreteTommy Y. Lo ?, H.Z. Cui 1, Abid Nadeem 1, Z.G. Li 1Department of Building and Construction, City University of Hong Kong, Hong KongReceived 31 July 2003;

2、accepted 23 June 2006AbstractAir entraining agent is used to control the floatation of lightweight aggregate (LWA) in lightweight aggregate concrete (LWAC), therefore reducing the segregation of LWAC. At the same time, u

3、sing an air entraining agent will affect the water sorption of the concrete. In this paper, two lightweight concrete mixes of density 1000 kg/m3 and air content of 13.5% and 31.9% were compared and the effects of entrain

4、ed air on the strength, surface sorptivity, and chloride permeability of LWAC are presented. Results show that the use of porous LWA would not lower the permeability resistance of concrete. Entrained air had little effec

5、t on sorptivity but a major effect on chloride permeability. The weaker pores' network in the cement paste is the basic cause for the high chloride permeability of concrete than the use of porous LWA. Although chlori

6、de permeability of low density LWAC concrete decreased with age of concrete, it was found that the concrete was not dense enough to stop the chloride ion to penetrate through the concrete before the concrete mature at 90

7、 days. © 2006 Elsevier Ltd. All rights reserved.Keywords: Lightweight concrete; Lightweight expanded clay aggregate; Sorptivity; Chloride permeability; Air content; Compressive strength1. IntroductionLow strength li

8、ghtweight concrete is used for prefabrication of dry partition walls, washing room and kitchen modules [1–3]. For lightweight aggregate concrete (LWAC), air entraining agent is used to control the floatation of lightweig

9、ht aggregate (LWA) therefore reducing the segregation of LWAC and lowering the density of the resulting concrete. However, the water sorption of the concrete will be increased at the same time. Past findings [4– 7] indic

10、ated that sorptivity can be correlated to permeability, and is a function of porosity, pore diameter, distribution and continuity of pores within the concrete matrix. In many cases, the chloride permeability of ordinary

11、concrete using AASHTO method [8] is used to compare the permeability of concrete but few researchers have studied the chloride permeability of LWAC. In this study, the effects of the entrained air on the strength, sorpti

12、vity and permeability of concrete of two LWAC mixes of density 1000 kg/ m3 will be studied. Results of the surface sorptivity and chloride permeability of concrete were analyzed.2. Materials and experimental details2.1.

13、Materials and specimens preparationThe binders used were Portland cement (OPC) to BS12:1989 [9], with Blaine surface area of 330 m2/kg and a density of 3150 kg/m3. The LWA was a lightweight expanded clay aggregate. Fine

14、and 10 mm coarse aggregates were of bulk densities of 955 kg/m3 and 403.8 kg/m3, respectively. The LWA was pre-wetted with half of the total gauging water for 30 min so that the aggregate was ‘surface saturated’ prior to

15、 mixing. Water absorption of 30 min of the fine and coarse aggregate is 14.5% and 5.4%, respectively. The mix propor- tions are summarized in Table 1. Two concrete mixes of the same w/c ratio but different air contents w

16、ere prepared. Liquid air entraining agent in accordance with BS4887 [10]was added to the concrete mix to control the floatation of LWA in the cement paste. The resulting fresh concrete had good workability and the floata

17、tion of lightweight aggregate and segregation of concrete were well controlled. For each concrete mix, four 100×100×100 mm3 cubes were prepared for test at each age. Three of them were for compressive test and

18、the last one was for sorption test. In addition, one discCement and Concrete Research 36 (2006) 1874–1878? Corresponding author. Tel.: +852 27887685; fax: +852 27887612. E-mail address: tommy@cityu.edu.hk (T.Y. Lo). 1 Te

19、l.: +852 27887685; fax: +852 27887612.0008-8846/$ - see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.cemconres.2006.06.009min0.5 at a w/c ratio of 0.6. Some other research studies sug- gested

20、 that OPC concrete with w/c ratio of 0.4–0.5 would have sorptivity of about 0.23 mm/min0.5 [19–22]. Therefore, the sorptivity value for these LWAC with low strength and air content at w/c ratio of 0.40 was not particular

21、ly high when compared to normal weight concrete of the same w/c ratio. As sorption is mainly through capillary pores, the similarity of water sorptivity of the mixes with different air content sug- gested that the pores

22、within the two concrete mixes were larger than capillary pores. However, the change of water sorptivity with age is different from that of normal weight concrete. For normal concrete, water sorptivity generally decrease

23、with the increase in age. In this research, sorptivity of LWAC increase with age. For Mix A, the sorptivity at 7 days was 0.122 mm/ min0.5 and it increases to 0.130 mm/min0.5 for 90 days. The similar phenomenon also occu

24、rs in Mix B. The main reason for this phenomenon was the application of the air entraining agent and the use of lightweight aggregate. The initial sorption (A) as per Table 2 increases with age of concrete indicated the

25、mean of the initial sorption for Mixes A and B of the LWAC changes from 0.444 mm, 0.66 mm to 2.465 mm at 7 days, 28 days and 90 days, respectively. It is clear that concrete sorption is closely related to the surface por

26、es of the concrete paste. The surface pore reduces as C–S–H and LWAC strength also develop with time. Accordingly, it reduces the permeability and water sorptivity of concrete. The above phenomenon can be attributed to t

27、he fact that the quantity of pores of Mix B is greater than that of Mix A due to the higher air content; the surface sorption of Mix B is higher at the early ages but becomes similar at 90 days. Since the cement contents

28、 of both Mixes A and B are the same, the cement hydration and the structure of capillary pore will be similar. This explains why in Fig. 4 the surface sorptions of the two mixes at the age of 90 days are similar. Moreove

29、r, it also induced that the effect of addition of air entraining agent to lightweightaggregate concrete on water sorptivity of the concrete became insignificant after 90 days.3.2. Chloride permeability of LWACChloride pe

30、rmeability of the LWAC at different ages was measured in terms of the current passing the concrete specimens (in A) versus time (in min). The total charges in terms of Coulombs are presented in Figs. 5–7. As seen in the

31、Figures, the currents passing through concrete mixes showed a rapid initial increase, reaching a peak value at around 30 min, and then dropped steadily with time. The current passing through Mix B is always higher than M

32、ix A because air content in Mix B is higher. The relationship between porosity and permeability of mortar and concrete has been explained by past researchers [23–25]. For concrete adding entraining air admixture, it can

33、be known that if the porosity is high and the pores are inter- connected the permeability is also high; on the other hand, if the pores are discontinuous the permeability of the concrete is low although the porosity is h

34、igh. Therefore, the chloride perme- ability of LWAC at the age of 90 days becomes more or less constant as seen in Fig. 7 when the average pore size reduced when the age of concrete increased. During the experiment, most

35、 of the cells reached the tem- perature of 88 °C before the standard duration of 6 h. Only theFig. 4. Sorptivity of LWAC at 90 days.Table 2 Water sorptivity of LWAC mixesLWAC mixes Water sorptivity (mm/min0.5) Initi

36、al sorption (mm3/min2)7-day 28-day 90-day 7-day 28-day 90-dayMix A (13.5%) 0.122 0.128 0.130 0.363 0.472 2.484 Mix B (31.9%) 0.116 0.124 0.132 0.526 0.847 2.447Fig. 5. Current of LWC RCPT at 7 days.Fig. 6. Current of LWC