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Vacuum concrete
Vacuum concrete is concrete which includes high water content during the mixing to facility the
mixing pro...
Technique and Equipment’s for Vacuum Concrete:
The main aim of the technique is to extract extra water from concrete surfa...
1- Gazi University, TechnicalEducationFaculty, Construction Department 28 August,
2009 mursel erdal
Use artificial neural ...
Figure.2
After 28-day period, Schmidt hammer test in which surface hardness is indirectly measured is
widely used for comp...
Next researchis about the some method of vacuum dewatering to improve strength
2- Shigemitsu Hatanaka Eisuke SakamotoNaoki...
A series of experiments using the proposedmethod
For the purposes ofdefining and improving the proposedmethod, we have con...
Table.1 factorand the level of experiments
Experiment no
factor
Sl (cm) Fc
(Mpa)
Specimen size (cm) Time of
dewatering
(mi...
Table .2 Mixing proportion of concrete
Fc(mpa) w/c % s/a % Unit mass (kg/m3) Sp/c % Sl(cm)
W c s G
10 80 52 195 243 945 88...
Experiment I: the effect of slump Diagram.1 show that the greater the slump the greater the
volume of discharged of water ...
Experiment II: the effect of strength level with (w/c) ratio Diagram.2 showthat the greater the
strength of the concreteth...
Experiment III: the effect of slab thickness Diagram.3 shows that the thicker the slab the
larger the volume of water disc...
Experiment IV: the effect of timing of the start of vacuums treatment Diagram.4 shows that
the later the timing of the sta...
Figure.5 schematic drawing of core specimen
Experiment I: The effects of slump: As shown in Diagram. 5, there was no signi...
Diagram.5
Diagram.5
20
18
20
25
20
21
24
35
20
18
16
15
0
10
20
30
40
First layer Second layer Third layer Fourth layer
co...
Experiment II: The effects of strength level (water/cement ratio): As shown in diagram.6
comparison of the compressive str...
Diagram.6 (20Mpa)
Diagram.6 (30Mpa)
18
20
21
25
18
20.5
23
33
18
16 16.5
14
0
10
20
30
40
First layer Second layer Third l...
Diagram.6 (40Mpa)
Experiment III: The effects of slab thickness: As shown in Diagram.7, the effects of vacuum
treatment ap...
Diagram.7
Experiment IV: The effects of the timing of vacuum treatment start: As shown in Diagram.8,
among the specimens t...
Diagram.8
In conclusion in these experiments, we only examined the change over time of vacuum strength
during vacuum treat...
technique are investigated by a series of tests. Based on test results, the new technique improves
concrete strength and o...
Figure.5 diagrammatic representation for new vacuum dewatering technique
Therefore, in the new technique, most of the work...
in molds of various dimensions (150 x 150 x 750 mm, 200 x 200 x 750 mm and 250 x250 x 750
mm) using single dewatering pipe...
relation between w/c ratio and extract water
this investigation investigate in compressive strength in different ages of s...
cement/aggregate ratio but with different water/cement ratios were cast in molds of
150x150mm, 200 x 200mm and 250 x250 mm...
Vacuum concrete
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Vacuum concrete

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Vacuum concrete

  1. 1. Vacuum concrete Vacuum concrete is concrete which includes high water content during the mixing to facility the mixing process and to improve the workability to enable it to be handled, placed into complicated moulds or around extensive reinforcement. Vacuum processed concretefirst invented by Billner in United state in 1935. This process is to reducing the final water /cement ratio of concrete before setting to controls strength and other properties of concrete. The advantage of this technique is: 1- Improve the compressive and tensile strength 2- Make concrete resistance to abrasion and impact 3- Make concrete resistance to the freeze-thaw 4- Reduce the shrinkage 5- Make lower permeability and greater durability One of the biggest disadvantage with the vacuum dewatering system is that it is best suited for the more traditional long strip method of construction which is fine when considering the construction of super flat floors for vacuum narrow aisle applications where the majority of the construction joints fall under the racking and out of reach from forklift traffic.
  2. 2. Technique and Equipment’s for Vacuum Concrete: The main aim of the technique is to extract extra water from concrete surface using vacuum dewatering. As a result of dewatering, there is a marked reduction in effective water-cement ratio and the performance of concrete improves drastically. The improvement is more on the surface where it is required the most. Mainly, four components are required in vacuum dewatering of concrete, which are given below: 1. Vacuum pump 2. Water separator 3. Filtering pad 4. Screed board vibrator Vacuum pump is a small but strong pump of 5 to 10 HP. Water is extracted by vacuum and stored in the water separator. The mats are placed over fine filter pads, which prevent the removal of cement with water. Proper controlon the magnitude of the water removed is equal to the contraction in total volume of concrete. About 3% reduction in concrete layer depth takes place. Filtering pad consists of rigid backing sheet, expanded metal, wire gauge or muslin cloth sheet. A rubber seal is also fitted around the filtering pad as shown in fig.1. Filtering pad should have minimum dimension of 90cm x 60cm. Fig. 1: Vacuum dewatering of concrete
  3. 3. 1- Gazi University, TechnicalEducationFaculty, Construction Department 28 August, 2009 mursel erdal Use artificial neural network and regression technique (ANN) to predict the compressive strength of vacuum concrete. In this research he built three different concretes were prepared by applying variable vacuum application duration. And use Windsor probepenetration test, Schmidt hammer test and pulse velocity determination tests on these concrete samples. Table.1 Mix proportion Amount Crushed coarse aggregate (16 - 25 mm) 334 kg Crushed medium aggregate (4 - 16 mm) 632 kg Crushed fine aggregate (0 - 4 mm) 761 kg Cement (CEM I 42.5) 426 kg Water 190 lt In this study, crushed limestone aggregate whose grain size distribution is given in Table 1, CEM I 42.5 Portland cement and ordinary water are used for sample preparation. Table 1 presents the grain size distributions of aggregate, cement and water amount for 1 m3 fresh concrete. Concrete mix was prepared according to C 20 type concrete, and slump of fresh concrete was about 20 cm. Duration of vacuum application was 34 min to first formwork, 17 min to second formwork. Vacuum was not applied to third formwork (Figure 2)
  4. 4. Figure.2 After 28-day period, Schmidt hammer test in which surface hardness is indirectly measured is widely used for compressive strength estimation and it has the advantage of being economical, fast and non- destructive. However this test only reflects the surface properties of concrete and it may not accurately estimate the internal strength. Because vacuum processed concretehas a higher surface hardness, performance of Schmidt hammer tests should be even worse for vacuum processedconcrete(Mehta, 1986; Erdal and Simsek, 2006). In addition to these popular nondestructive test methods, a relatively new technique called as Windsor probepenetration test is also utilized for the estimation of compressive strength. In this method, compressive strength is indirectly estimated using the penetration of a probein to the concrete, which is charged with explosives. Lesser the depth of penetration of the probemeans the higher the compressive strength of concrete (Mallick, 1983; Windsor ProbeTest System Inc., 1994) In this method they used RMSE calculation theorem and compare with others research that have predict years ago and then with this materials they predicted the compressive strength. RMSE=√ 𝟏 𝐧 ∑ (𝐟𝐜 𝐞𝐬𝐭 − 𝐟𝐜 𝐦𝐞𝐚) 𝟐𝐧 𝟏 𝟐 Conclusion: in this study performances of previously suggested single and multi variable equation used for the estimation of compressive strength of concreteutilizing nondestructive test results were compared.
  5. 5. Next researchis about the some method of vacuum dewatering to improve strength 2- Shigemitsu Hatanaka Eisuke SakamotoNaokiMishima Akio Muramatsu 3march 2007 Improvement of strength distribution inside slab concrete by vacuum dewatering method (1)In this documents the investigation investigated on the surface of concrete floor slab to improve strength. It has been reported that in the conventional method the duration of dewatering is 20–30 min, suchthat approximately 50% of the total volume of water is extracted within 5 min after the beginning of dewatering and almost no effect is apparent later than 30 min after the beginning. The effects of slab thickness have also been examined, and it seems that the final dewatering rate is not closely associated with slab thickness. Figure.3 Figure.3 Water/cement ratio distribution of concrete was examined immediately after vacuum treatment; a conspicuous drop in water/cement ratio was detected in the upper layer. It is known that the lower cement content of concrete increases the difference in the water/cement ratio between the upper and lower layers. Also, it is said that the more upper the layer the greater the distributional gradient of water/cement ratio of concrete in the direction of depth. (1) Lay the concrete and level its surface carefully using a ruler (see Fig. 2a). If any aggregate is exposed on the concrete surface, the degree of vacuum will be low. 
 (2) At almost the end of bleeding, lay a bottomsheet (e.g. about 1 m wide and 5 m long). The bottom sheet should be 15 cm away from each edge of the construction area. Note that the most important key point for the proposedmethod is just to wait till the end of bleeding before the operation. 
 (3) Lay a top sheet to cover the bottomsheet (see Fig. 2b). To keep the degree of vacuum high, the top sheet should be free of wrinkles. 
 (4) Start vacuum dewatering (see Fig. 2c). Continue vacuum dewatering for about 5 min at a degree of vacuum of 60% or higher. 

  6. 6. A series of experiments using the proposedmethod For the purposes ofdefining and improving the proposedmethod, we have conducted a series of experiments on the following themes: Experiment I, the effects of slump; Experiment II, the effects of strength level; III, the effects of slab thickness; and IV, the effects of the timing of the start of vacuum treatment (Table 1). This section reports the results of the experiments, focusing on the volume of dewatering, rebound number on the surface, and internal strength distribution. (2)The timing of the start of dewatering was determined to be 120 min after concrete placing, that is, the approximate time of completion of bleeding. Also, in order to measure surface hardness, no coating agents were sprinkled.
  7. 7. Table.1 factorand the level of experiments Experiment no factor Sl (cm) Fc (Mpa) Specimen size (cm) Time of dewatering (min) Time of experiment (month) Performance of vacuum Measurement items Top surface Slab thickness Experiment I 8,18 20 60 × 40 24 30,120 9 100v,200w 40 1/min Discharge volume of bleeding water Solid content in the discharged water Compressive strength in 28 day core with diameter 5*5cm in height Experiment II 18 10,20, 30,40 100v,200w 60 1/min Experiment III 20 46 × 30 12,18,24 120 8 Experiment IV 18 0,30,60, 120,240 11 Table .1 this table show the experimental condition Table .2 shows the mix proportion for each concrete series. Concrete compaction was performed using a vibrating bar and a wet compress was applied for curing in laboratory. Table 3 shows the atmospheric conditions at each concrete placing, and the mean outdoors temperature and humidity during each curing. Of the measurement items shown in Table 1, discharged water volume represents the volume of water suctioned by vacuum treatment.
  8. 8. Table .2 Mixing proportion of concrete Fc(mpa) w/c % s/a % Unit mass (kg/m3) Sp/c % Sl(cm) W c s G 10 80 52 195 243 945 884 .2 18 20 65 50 180 277 913 927 .3 8 185 285 904 917 .4 18 30 55 49 180 327 874 924 .5 40 40 47 175 438 802 918 .6 Fc: target compressive strength; W*/C: water/cement ratio; W*: (water + super plasticizer (SP)); s/a: sand S: sand; G: coarse aggregate; SL: target slump Table. 3 atmospheric conditions in the experiments Type of experiment Day of concrete placing (in lab) Mean during curing period (outdoor) Weather Temorature © Humidity% Tempratue© Humidity% Experiment I Sl: 8cm Fair 25 56 19 72 Sl: 18cm Fair 17 41 8 61 Experiment II Fc: 10 Cloudy 27 89 24 75 Fc: 20 Fair 17 41 8 61 Fc: 30 Fair 18 62 15 62 Fc: 40 Cloudy 26 82 25 76 Experiment III Cloudy 28 77 25 79 Experiment IV Fair 18 62 9 62
  9. 9. Experiment I: the effect of slump Diagram.1 show that the greater the slump the greater the volume of discharged of water (surface area of specimen 0.24m2) SL 8 cm SL 18 cm 0 0.5 1 1.5 2 2.5 no treatment treatment after 30 min treatment after 120 min 14.8% 12.9% 20.2% 18.1% SL 8 cm SL 18 cm
  10. 10. Experiment II: the effect of strength level with (w/c) ratio Diagram.2 showthat the greater the strength of the concretethe smaller the volume of water discharge when vacuum treatment was carried out was 2-fold (10, 20, and 30 MPa levels) to 5-fold (40 MPa level) larger than the volume of water discharged when no vacuum was applied. (Surface area of specimen 0.24m2) 40 mpa 30 mpa 20 mpa 10 mpa 0 0.5 1 1.5 2 2.5 no treatment treatment after 30 min treatment after 120 min 4.8% 4.2% 14.8% 13.2% 20.2% 18.1% 20.3% 18.3% 40 mpa 30 mpa 20 mpa 10 mpa
  11. 11. Experiment III: the effect of slab thickness Diagram.3 shows that the thicker the slab the larger the volume of water discharged, and that the volume of water discharged correlated approximately to the volume of the concrete. However, regarding the specimen with slab thickness of 12 cm, the dewatering rate was rather low at 12.2% (surface specimen 0.14m2) For example: for 12cm specimen 2lt/m3 dewatering for 18cm specimen 3.9lt/m3 and for 24cm specimen 4.7lt/m3 dewatering vacuum dewatering no treatment 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 24 cm 18 cm 12 cm 14.2% 15.8% 12.2% vacuum dewatering no treatment
  12. 12. Experiment IV: the effect of timing of the start of vacuums treatment Diagram.4 shows that the later the timing of the start of vacuum treatment, the smaller the volume of water discharged, with the exception of the specimen in which vacuum treatment was carried out immediately after concrete placing (0 min). It seems that the reason why the volume of water discharged by the specimen in which vacuum treatment was started 0 min after concrete placing was smaller than that of the specimen in which vacuum treatment was started 30 min after the completion of concrete placing is that immediately after concrete placing, the bleeding water had not begun to reach the upper segments of the concrete. (surface area of specimen 0.14m2) Distribution of internal strength Diagram 5-8 shows the distribution of compressive strengths inside the slab specimen. These figures use the compressive strength obtained for the 5 cm (diameter) · 5 cm (height) core specimens excised from the slab specimen. As shown in these figures, the general tendency was for specimens without treatment, the higher the layer the lesser the compressive strength, whereas for specimens that was subjected to vacuum treatment the higher the layer the greater the compressive strength.( Figure .5) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 min 30 min 60 min 120 min 240 min no treatment 19.5% 20.6% 19.2% 17.8% 14.9% Vacuum treatment no treatment
  13. 13. Figure.5 schematic drawing of core specimen Experiment I: The effects of slump: As shown in Diagram. 5, there was no significant difference in compressive strength at the uppermost layer (4th layer) between specimens with slumps of 8 and 18 cm. In general, in the case of the specimen with slump of 18 cm, the compressive strength increased gradually towards the upper layer, whereas in the case of the specimen with slump of 8 cm, the compressive strength did not change much up to the third layer and sharply increased at the 4th layer. Regarding the effects of the timing of treatment, for specimens with any degree of slump, the compressive strength was greater for treatment after 120 min than for treatment after 30 min, and the higher the layer the more conspicuous was the difference.
  14. 14. Diagram.5 Diagram.5 20 18 20 25 20 21 24 35 20 18 16 15 0 10 20 30 40 First layer Second layer Third layer Fourth layer compresive strength after 30 min after 120 min No treat ment 17 20 22 25 17 20.5 23 32 17 15 14 12 0 10 20 30 40 First layer Second layer Third layer Fourth layer compresive strength after 30 min after 120 min No treat ment
  15. 15. Experiment II: The effects of strength level (water/cement ratio): As shown in diagram.6 comparison of the compressive strength of the uppermost layer between a specimen that was subjected to vacuum treatment 120 min after the completion of concrete placing and another specimen that was not subjected to treatment showed that the compressive strength in the former was greater by about 15–20 MPa, regardless of the strength level. (3)Furthermore, for any strength level, the compressive strength was greater in the specimen that underwent vacuum treatment 120 min after the completion of concrete placing than in the specimen that underwent vacuum treatment 30 min thereafter, and the higher the layer the more conspicuous was the difference. Diagram.6 (10 Mpa) 12 13 14 19 12.5 15 17 22 11 10.5 10.2 9.8 0 10 20 30 40 First layer Second layer Third layer Fourth layer compresive strength after 30 min after 120 min No treat ment
  16. 16. Diagram.6 (20Mpa) Diagram.6 (30Mpa) 18 20 21 25 18 20.5 23 33 18 16 16.5 14 0 10 20 30 40 First layer Second layer Third layer Fourth layer compresive strength after 30 min after 120 min No treat ment 36 37 39 42 36.5 38 43 49 32 31 30.5 30.5 0 10 20 30 40 50 60 First layer Second layer Third layer Fourth layer compresive strength after 30 min after 120 min No treat ment
  17. 17. Diagram.6 (40Mpa) Experiment III: The effects of slab thickness: As shown in Diagram.7, the effects of vacuum treatment appear to depend on the distance from the surface, regardless of slab thickness. Comparison of the internal strength distributions of specimens with slab thickness of 24 cm showed that the compressive strength of the lowermost layer was similar regardless of whether or not the specimen underwent vacuum treatment. Therefore, it is assumed that the dewatering effect is valid up to about 15 cm from the upper part of the specimen. This interval is somewhat shorter than that of about 25 cm. In the specimens with slab thickness of 12 and 18 cm, the compressive strength at the lowermost layer was increased by vacuum treatment, and the thinner the slab thickness the more conspicuous the increase in compressive strength. The internal strength of the specimen that was not subjected to vacuum treatment with slab thickness of 12 cm was about 4 MPa less than that of other specimens that were not subjected to vacuum treatment; one reason for this may be the effect of compaction. 45 46 46.5 48 45.5 47 50 53 45 45 44 42 0 10 20 30 40 50 60 First layer Second layer Third layer Fourth layer compresive strength after 30 min after 120 min No treat ment
  18. 18. Diagram.7 Experiment IV: The effects of the timing of vacuum treatment start: As shown in Diagram.8, among the specimens that underwent vacuum treatment, the largest difference in compressive strength (12 MPa) between the uppermostand lowermost layers was seen in the specimen that underwent vacuum treatment after 120 min; in other specimens the difference was about 7–9 MPa (excluding those that underwent vacuum treatment after 240 min). Regarding the specimens that underwent vacuum treatment after 240 min, the compressive strengths at the middle layer and lower layer were almost the same as those that were not subjected to vacuum treatment, and the compressive strength at the upper layer was less than the compressive strengths of the specimens that underwent vacuum treatment at other time-points. In this experiment, bleeding had already been completed and cementation of the concrete began 240 min after concrete placing. Therefore, we assume that the effects of dewatering and compaction did not influence the internal zones of the concrete, even with vacuum treatment (see Diagram.4).
  19. 19. Diagram.8 In conclusion in these experiments, we only examined the change over time of vacuum strength during vacuum treatment, while the effects of vacuum strength on the dewatering rate, surface hardness, and compressive strength distribution are expected to be considerable. Next researchis about the some new method of vacuum dewatering, means Study a new technique for producing Vacuum-dewateredconcrete 3 - Department of Building & Construction Technology Engineering, Technical College / Mosul, Iraq In this work, investigate a new technique for producing vacuum-dewatered concrete. Perforated PVC pipes incased in cottoncloth are used in this technique to dewater concrete from inside of concrete volume, rather than from the surface, as is the case in the conventional vacuum dewatering method. These pipes are laid in position inside concrete forms, and a vacuum pump is connected to the dewatering pipes, which is operated after casting of fresh concrete to remove the excessive water from which. Properties of vacuum dewatered concrete using the new
  20. 20. technique are investigated by a series of tests. Based on test results, the new technique improves concrete strength and other mechanical properties particularly at early ages. The new dewatering technique is a good alternative to the conventional vacuum dewatering technique and can have a wider range of practical applications than the conventional method. This technique is processed from inside of the freshly placed concrete rather than surface through perforated PVC pipes encased in muslin (cottoncloth) to prevent the removal of cement and other fine particles with water. These pipes are embedded and fastened in place in forms via reinforcement bars or any other means, a steel bar or wire can be inserted inside the PVC pipes to give the required stiffness, keep alignment, facilitate bending and prevent pipes from clogging due to external pressure during vacuum process.Figure.4 Figure .4: cross-section of perforated dewatering pipe The dewatering system can be multiple pipes connected directly to the vacuum pump or a net of interconnected pipes connected to the vacuum pump. A diagrammatic representation of the method is shown in Fig. 5
  21. 21. Figure.5 diagrammatic representation for new vacuum dewatering technique Therefore, in the new technique, most of the work is done during preparation for casting and minimum time is consumed during vacuum dewatering. Use this technique in laboratory, new vacuum dewatering technique applied by plywood molds figure.6 Figure.6 The materials used in this investigation were ordinary Portland cement (OPC) type 1, river sand of gradation F according to BS EN 882 and fineness modulus of 2.18, and river coarse aggregate of 20mm maximum size. Specific gravity of fine and coarseaggregates was 2.63 and 2.65 respectively. Clean tap water was used in all mixes. Electrical vacuum pump of 1.5 kW power producing vacuum pressureof 60mm of mercury was used in all tests. Concrete was cast
  22. 22. in molds of various dimensions (150 x 150 x 750 mm, 200 x 200 x 750 mm and 250 x250 x 750 mm) using single dewatering pipes laid along center of mold section. Mix proportions of all mixes was (1 cement: 2.5 sand: 3.5 coarseaggregate) by weight. To study the effect of dewatering pipe characteristics, Pipes with three different outside diameters (6, 10 and 14 mm) and of 1.5 mm wall thickness were used. The number of perforations was 12, 16 and 20 holes per 100 mm of dewatering pipe in all pipe sizes. The holes were 2mm diameter and uniformly distributed on the pipe surfaces. The size of test specimens was 150x150 in cross section and 750 mm long. The effect of spacing of dewatering pipes and water/cement ratio on efficiency of the process and properties of concrete produced, molds of different sizes were used. Molds were of dimensions: 150 x 150 mm, 200 x 200mm and 250 x250 mm in section and 750mm long. The effect of spacing of dewatering pipes and water/cement ratio on efficiency of the process and properties of concrete produced, molds of different sizes were used.. Figure.7 show the vacuum dewatering time relation with w/c ratio Figure.7 When the water extract, means that firstly the capillary diameters in the cement paste decrease as the water-cement ratio decreases in fresh concrete near dewatering pipes. Secondly, hydration and setting of cement paste at later times reduces capillary diameters as well. Thus, it is considered that vacuum processing during 40 minutes is practical and economical and is used in all subsequenttests.
  23. 23. relation between w/c ratio and extract water this investigation investigate in compressive strength in different ages of sample that vacuum with different w/c ratio shown in figure.8 Relation with flexural strength Effect of spacing of dewatering pipes on compressive strength of coresamples taken from vacuum processedand unprocessed (control) concretes at 28 days of age. Four mixes of same
  24. 24. cement/aggregate ratio but with different water/cement ratios were cast in molds of 150x150mm, 200 x 200mm and 250 x250 mm in cross section and 750mm long, using single dewatering pipe laid along center of each mold section. Specimen sectional dimensions, as discussed earlier, represent spacing of dewatering pipes in larger concrete sections to be used in practice show in this table. In conclusion this study a new vacuum dewatering technique is used to extract excess water from inside of concrete volume rather than the surface, Based on tests conducted to study the parameters affecting practical considerations and properties of concrete produced by the proposedmethod to improve compressive and flexural strength of concrete. And many other factor that investigate in this process suchas many method in many company that work in filed but every research is about improve the strength of properties of concreteto derive acceptable result in concrete. Refrence; 1-Malinowski R. and Wenader H., (1975), "Factors determining characteristics and composition of vacuum dewatered concrete", J. Amer. Concr. Inst., 72, pp. 98–101 
 [2]. NevilleA.M.,(2011),PropertiesofConcrete,5thEdition,LongmanScandTechPublishers. 
 [3]. Wenander,H.,(1975)."Vacuumdewateringisback".Concr.Construct.20:pp.40-42 
 [4]. Maloe P. G. (1999), "Use of permeable formwork in placing and curing concrete", Technical Report, Engineer Research and 
 Development Center, U.S.A. 
 Nakazawa T,Tanigawa K, Kurosaki T (1990) Effect of vacuum treatment on strength of concrete. Cement Sci Concrete Technol 44:342–347 (in Japanese) 5. Yang C, Wang Y, Jiang Z, Gu L (1991) Application of vacuum dewatering technique on casting concrete floors. 6. Lewis RK, Mattison EN, Smith CJ (1973) The vacuum dewatering concrete,CSIRO,Report 6 
 7.Malinowski R, Wenander H (1975) Factors determining characteristics and composition of vacuum dewatered concrete.

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