effects of vibration time on strength of ordinary and high

Effects of Vibration time on Strength of Ordinary and High Performance

Concrete

M. Emin ARSLAN Ercan YOZGAT Selim PUL Metin HUSEM

Department of Civil Engineering, Karadeniz Technical University, Trabzon/Turkey

http://www.ktu.edu.tr

Abstract- Strength, durability in other word performance of concrete has been increasing by the help of developing technology since it was started to use. It is easier to place fresh concrete by using chemical additives. However, vibration is needed to place fresh concrete in the mould correctly. Furthermore fresh concrete produced according to desired properties is placed either more or less, because of unsuitable vibration applications. This situation causes differences in compressive strength of concrete even if concrete is produced appropriately. In this study, effects of vibration time on concrete strength are experimentally investigated on ordinary and high performance concrete which are produced and used commonly. Finally optimum vibration times are tried to determine. Key-Words: -Normal strength concrete, high strength concrete, vibration, compressive strength, optimum vibration

time, fresh concrete

1 Introduction

Concrete is composite material commonly used in construction defined as composed of aggregate (coarse and fine), water, cement and sometimes chemical and/or additives[1]. Concrete which is used in prefabricated or cast in place reinforced concrete construction should have some properties such as strength and durability. This is why, materials used for producing concrete should be chosen suitable for purpose. One the most important reason of collapsing reinforced concrete structures during recent earthquakes is lower compressive strength of concrete[2]. Concrete strengths have deviations for each production, since it is composite material. During producing, placing and curing of concrete required attention should be paid to have desired properties. For this reason compressive strength which is one of the most important properties of concrete depends on material qualities and its proportion. Recent earthquakes have had concrete producers produce concrete more systematically, consciously and controlled. However, fresh concrete produced according to desired properties is placed either more or less, because of unsuitable vibration applications. As a result compressive strength

differences occur even if concrete is produced appropriately[1-7]. In this study, effects of vibration time on concrete strength are experimentally investigated on ordinary and high performance concrete which are produced and used commonly. Finally optimum vibration times are tried to determine.

2 Experimental Study

2.1 Materials

Maximum size of aggregate used for producing ordinary and high performance concrete was 16 mm. Physical properties and proportion of aggregates are given in Table 1 and Table 2, respectively. CEM II A-P/32.5 R for ordinary concrete and CEM I A-P/42.5 R for high performance concrete were used as cement.

Recent Researches in Geography, Geology, Energy, Environment and Biomedicine

ISBN: 978-1-61804-022-0 270

Table 1 Physical Properties of Aggregate

Aggregate Saturated Specific Gravity (kg/m3)

Water Absorption

(%) Course 2640 1.45

Fine 2730 1.63 Table 2. Proportion of Aggregates

Sieve No

16-8 mm

8-4 mm

4-2 mm

2-1 mm

1-0.5 mm

0.5-0.25 mm

% 30 20 20 10 10 10 2.2 Mixture Proportion and Producing of Concretes

Eight different W/C ratios were used for producing concretes. Mixture proportion of ordinary and high performance concrete are given in Table 3. Table 3. Mixture proportions of concretes

Series No

W/C Cement (kg/m3)

Water Aggregate (kg/m3)

For ordinary concrete A 0.65 350 228 1693 B 0.60 350 210 1741 C 0.55 350 193 1685 D 0.50 350 175 1845

For high strength concrete E 0.45 500 225 1574 F 0.40 500 200 1640 G 0.35 500 175 1707 H 0.30 500 150 1773

A concrete mixer having 120 liter capacity was used to produce. Each size of aggregate was weighted and put into mixer moisturized in advance and mixed for 3 min. After that saturation water was added and mixed 3 min. Thereafter, mixture was mixed another 3 min. by adding mixing water without stopping (Fig. 1). Finally produced concrete was poured into 150 mm cube casts and every 3 of each are individually subjected to 10, 20, 30, 40, 60, 90, 120, 180 and 240 seconds vibrations (Fig 2). In this way 27 ordinary concrete and 27 high performance concrete specimens were produced. After one day, concrete specimens were taken out of the casts and cured in water tank maintained at 22 °C± 2 °C for 28 days (Fig.3 and Fig 4).

Figure 1. Fresh Concrete in moulds Figure 2 Vibration table Figure 3. Curing of ordinary and high strength concrete Figure 4 Compressive test on concrete samples


ISBN: 978-1-61804-022-0 271

3 Results and Discussion In this study, effects of vibration time on strength of ordinary and high performance concrete were investigated. Test results are given in Table 4. Table 4 Change of compressive strength with vibration time

It is clearly seen in Table 4 compressive strength of ordinary concrete and high strength concrete decrease when W/C increases. In addition vibration time is another situation affecting strength of concretes. When W/C ratio increases and at the same time vibration time extends, strength of concretes decrease. Similarly fallen W/C and short vibration time cause to decreasing on concrete strength as well. Relations between vibration time and compressive strength of concrete are given in Fig 3, Fig. 4, Fig 5, Fig 6, Fig 7, Fig 8, Fig 9, Fig 10 and Fig 11 according to water-cement ratio .

Figure 3. Compressive strength- vibration time relation for W/C ratio 0.65

Figure 4 Compressive strength- vibration time relation for W/C ratio 0.60



W/C ratio

Vibration time (second) 10 20 30 40 60 90 120 180 240

Ordinary concrete 0.65 20 21 19 21 22 19 17 16 14 0.60 24 26 26 24 26 26 24 22 19 0.55 23 24 24 27 29 28 26 24 22 0.50 25 27 28 30 32 31 29 27 24

High strength concrete 0.45 51 52 54 53 53 51 50 48 48 0.40 53 57 58 56 57 57 56 54 52 0.35 61 60 64 63 61 62 60 58 56 0.30 72 72 76 74 75 73 70 70 68


ISBN: 978-1-61804-022-0 272




Figure 10 Compressive strength- vibration time relation for W/C ratio 0.30 It is seen in the figure that 60 s vibration time is optimum for ordinary concrete depending on W/C ratios (0,65, 0.60, 0.55 and 0.50). It is seen that 30 s vibration time is optimum for high performance concrete. Reason of this situation is that high performance concrete was produced using high quality cement and higher dosage, super plasticizer for obtaining workable mixture and fine pozzolanic additive such as micro silica.

4 Conclusion In this study effects of vibration time on concrete strength were experimentally investigated on ordinary and high performance concrete which are produced and used commonly. Some conclusions obtained from this study are given below. 1) When W/C ratio increases, extended vibration time

negatively affects strength of ordinary concrete. Reason of this situation is that increasing W/C ratio causes fluid concrete, therefore extended vibration time brings about segregation of course aggregates.

2) Optimum vibration time for ordinary concrete is

determined as 60 s. Vibration times longer or less than 60 s decrease compressive strength. Even compressive strengths of samples subjected to 240 s vibration time are approximately 36% lower than those of 60 s vibration time depending on W/C ratios.

3) On the contrary to ordinary concrete, optimum

vibration time for high performance concrete


ISBN: 978-1-61804-022-0 273

shorter and its value is 30 s. Reason of this situation is that high performance concrete was produced using high quality cement and higher dosage, super plasticizer for obtaining workable mixture and fine pozzolanic admixture such as micro silica.

4) Compressive strength of high performance concrete

is change with W/C ratio and vibration time as well. However, high performance concrete is affected by vibration time changes less than ordinary concrete. For instance, strength loss of samples subjected to 240 s vibration time 11% in proportion to samples with 30 s vibration time. This result can be explained that usage of fine materials in composition and super plasticizer increase cohesion of concrete.

Briefly, appropriate vibration time and its application are important to obtain desired concrete, even if it is produced with high quality materials and attentively.

References

[1] Neville AM., Properties of concrete., Pearson Education Limited, Fourth Edition, Edinburg, England, 2008.

[2] Durmus A, Dogangun A, Husem M, Pul S. The Report of Investigation of 17 August 1999 Kocaeli Earthquake in terms of Civil Engineering. Turkish Chamber of Civil Engineers, 1999, 54p. Trabzon-Turkey.

[3] Safawi MI, Iwaki I., Miura T., The segregation tendency in the vibration of high fluidity concrete. Cement and Concrete Research, 34, 2 (2004) 219-226.

[4] Hughes BP., The workability of concrete subjected to vibration. Cement and Concrete Research, 2, 1 (1872) 101-102.

[5] Erdogan YE., Materials of construction. Metu Press, Ankara, Turkey, 2002.

[6] Husem M, Durmus A. Comparing the behavior of Lightweight and Ordinary Concrete. Proceedings of the Second International Conference in Civil Engineering

on Computer Applications, Research and Practice, University of Bahrain, 1996.

[7] Akman MS, Materials of construction., ITU Press, Đstanbul, Turkey, 1987.


ISBN: 978-1-61804-022-0 274

effects of vibration time on strength of ordinary and high

Documents