Embed Size (px)
Citation preview
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 concrete first 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.
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 control on 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
1- Gazi University, Technical Education Faculty, 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 probe penetration 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)
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 concrete has a higher surface hardness, performance of Schmidt hammer tests should be even worse for
vacuum processed concrete (Mehta, 1986; Erdal and Simsek, 2006). In addition to these popular nondestructive test methods, a relatively new technique called as Windsor probe penetration test
is also utilized for the estimation of compressive strength. In this method, compressive strength is indirectly estimated using the penetration of a probe in to the concrete, which is charged with
explosives. Lesser the depth of penetration of the probe means the higher the compressive strength of concrete (Mallick, 1983; Windsor Probe Test 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 concrete utilizing nondestructive
test results were compared.
Next research is about the some method of vacuum dewatering to improve strength
2- Shigemitsu Hatanaka Eisuke Sakamoto Naoki Mishima 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, such that 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 bottom sheet (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 proposed method is just to wait till the end of bleeding before the operation.
(3) Lay a top sheet to cover the bottom sheet (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.
A series of experiments using the proposed method
For the purposes of defining and improving the proposed method, 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.
Table.1 factor and 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.
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
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 30min treatment after 120
min
14.8%
12.9%
20.2%
18.1%
SL 8 cm
SL 18 cm
Experiment II: the effect of strength level with (w/c) ratio Diagram.2 show that the greater the strength of the concrete the 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 30min 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
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 treatment0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
24 cm18 cm
12 cm
14.2%
15.8%
12.2%
vacuum dewatering
no treatment
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
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.
Diagram.5
Diagram.5
2018
20
25
2021
24
35
2018
1615
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
2022
25
17
20.5
23
32
1715
1412
0
10
20
30
40
First layer Second layer Third layer Fourth layer
compresive strength
after 30 min after 120 min No treat ment
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)
1213
14
19
12.5
1517
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
Diagram.6 (20Mpa)
Diagram.6 (30Mpa)
1820
21
25
18
20.5
23
33
1816 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 3739
42
36.538
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
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 46.548
45.547
5053
45 45 4442
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
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 uppermost and 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).
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 research is about the some new method of vacuum dewatering, means Study a new
technique for producing Vacuum-dewatered concrete
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 cotton cloth 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
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 (cotton cloth) 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 ins ide 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
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 coarse aggregates 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 pressure of 60mm of mercury was used in all tests. Concrete was cast
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 coarse aggregate) 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 subsequent tests.
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 core samples taken from
vacuum processed and unprocessed (control) concretes at 28 days of age. Four mixes of same
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 proposed method to improve compressive and flexural strength of concrete.
And many other factor that investigate in this process such as many method in many company that work in filed but every research is about improve the strength of properties of concrete to
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", Technica l 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.
