Effect of Aggregate to Binder Ratio on Shrinkage and Creep ...American corporation built concrete...

International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol: 11 No: 06 54

113206-7575 IJCEE-IJENS © December 2011 IJENS I J E N S

Abstract - High performance lightweight concrete, HPLC, could be considered as a combination between high performance concrete and structural lightweight concrete. In the present work, HPLC was produced from totally local materials (Metakaolin and Porcelinite). An experimental part had carried out to investigate the effect of increasing lightweight aggregate volume on time-dependent deformations of high performance lightweight concrete. The tests included in this work were: 28-day oven dry density, compressive strength, shrinkage strain, and creep strain in compression. The test period for shrinkage and creep was extended to 364 days. It was concluded that using higher Porcelinite to binder ratios had always negative effect on shrinkage of HPLC. Mix M20 (with 20% increase in P/B ratio) showed the lowest shrinkage magnitude and rate. No significant decrease was observed in specific creep of the tested mixes when adopting higher P/B ratios. Index Terms - Creep, Internal curing, Metakaolin, Porcelinite, Shrinkage.

I. INTRODUCTION

STRUCTURAL lightweight concrete, SLC, had been used successfully for many years for structural members and systems in buildings and bridges. In addition to its lighter weight, which permits saving in dead load, and thus reducing the costs of both superstructure and foundation, it is more resistant to fire and provides better heat and sound insulation than concrete of normal density [1], [2]. The first use of high strength lightweight concrete, HSLC, according to ACI 213 [2], was during World War I, when an American corporation built concrete ships with strength of 35 MPa. The term "high strength" in case of LWC is not related to the strength, but to the relation of strength to density. For all HSLC, high strength mortar matrix is used so that in general the concrete strength will be limited by the efficiency of aggregate.

Manuscript received November 5, 2010. Dr. Tareq S. Al-Attar is an Assistant Professor of Civil Engineering, with the University of Technology, Baghdad, Iraq. (mobile no: +964 790 1 454849, email:[email protected]). Dr. Jafa’ar S. Al-Sakini is a Lecturer in Civil Engineering with the Technical College, Baghdad, Iraq. (email:[email protected]).

This fact induces a very brittle behavior, which is independent of the strength. The stress-strain behavior of HSLC in compression is, generally, characterized by a linear ascending branch, a lower E-modulus and less ductility in the post failure region. These characteristics are usually more pronounced with increasing compressive strength and decreasing oven dry density. Therefore HSLC not only comprises LWC with a high strength, but also LWC with a low density [3]. High performance lightweight concrete, HPLC, can be thought as a combination between high performance concrete and structural lightweight concrete [4]. Only some of the characteristics of HPLC have a direct relationship to initial costs. For instance, the lower dead weight of HPLC means less expense due to materials movement on site. HPLC for structural purposes can be made on site or at a pre-casting site, generally by conventional techniques, so that wage costs are comparable to these for dense concrete. The modulus of elasticity (E value) is lower than that of dense concrete of comparable grade, and shrinkage and creep values are generally higher by comparison. But these do not necessarily mean that the serviceability of a lightweight concrete structure would be more adversely affected rather in circumstances such as the structure being subjected to thermal restraint or differential settlement, there would be a distinct advantage of lesser cracks and hence improvement of serviceability [5]. In addition to the aforementioned characteristics, lightweight aggregate with high internal moisture content may provide internal curing in high performance concrete which is often vulnerable to self-desiccation due to adopting low water to binder ratio [6]. The benefits of internal curing are increasingly important when pozzolans (silica fume, fly ash, Metakaolin, calcined shales, clays, and lightweight aggregate fines) are included in the mixture. It is well known that pozzolanic reaction is contingent upon theavailability of moisture. Additionally, internal curing would minimize the plastic(early) shrinkage due to rapid drying of concrete exposed to unfavorable drying conditions [2], [7]. Generally, deformation properties of concrete are affected by aggregates through a combination of the effects of water demand, aggregate stiffness, volume concentration, and paste-aggregate interaction [8]. And in particular with respect to time-dependent deformations (shrinkage and creep) of HPLC, Lopez [9] stated that there are few studies concerning these

Effect of Aggregate to Binder Ratio on Shrinkage and Creep of High Performance

Lightweight Concrete

Tareq S. Al-Attar, and Jafa’ar S. Al-Sakini



deformations which makes difficult to draw conclusions about HPLC performance.

II. RESEARCH SIGNIFICANCE

The aggregate volume in the mix is considered a major factor due to its restraining effect on time-dependent deformations (shrinkage and creep). Lightweight aggregate, would offer less restraint and may cause these deformations to be larger than normal aggregate due to its lower modulus of elasticity. On the other hand, increasing the lightweight aggregate volume, which has lower density, in the mix would reduce the paste volume and hence could cause shrinkage and creep strains to be smaller.

III. EXPERIMENTAL WORK

A. Materials Iraqi ordinary Portland cementconforming to the ASTM C150-02 (Type I) [10] was used. The supplementary pozzolanic material was Metakaolin and conforming to the ASTM C618-03 (Type N) [11]. It was added by 8 percent as partial replacement of cement. Table 1 shows chemical composition and some physical properties of both cement and Metakaolin. The used fine aggregate was natural sand with fineness modulus of 2.45. Local natural Porcelinite stones were used as lightweight coarse aggregate. It was received in lumps. The lumps were crushed with a jam crusher which was set-up to give a finished product of about 12.5 mm maximum aggregate size. Some physical properties of Porcelinite are shown in Table 2. Porcelinite was soaked until saturation (reaching constant weight) then, before mixing by about 2 hours, it was spread inside the laboratory in order to bring the aggregate particles to saturated surface-dry (SSD) condition. Sikament R2002, a high range water reducing agent with a set retarding effect, was used. This admixture was conforming to the ASTM C494-99 (Type G) [12]. B. Concrete Mixes One reference concrete mix, M0, was prepared according to the recommendations of the ACI 211 [13]. The average required strength at 28 days was 40 MPa and the water/binder (W/B) ratio was 0.28 by weight. The Porcelinite/binder (P/B) ratio was 2.0 by volume. Another two mixes, M10 and M20, were made by only increasing P/B ratio to 2.20 and 2.40 by volume (i.e. 10 and 20 percent increase). The fine aggregate content for all mixes was kept constant to magnify the effect of coarse lightweight aggregate only on the studied characteristics. Table 3 shows mix details. Standard ASTM procedures were used for casting and curing concrete specimens (100×100×100 mm cubes for compression test, 100×200 mm cylinders for density, creep tests, and 100×100×400 mm prisms for shrinkage test). C. Testing Procedures The testing program was extended to the age of 364 days. The conducted tests were as follows:

1. 28-day dry density (ASTM C 567-00) [14]. 2. Compressive strength (ASTM C 39-01) [15].

3. Shrinkage strain or length change (ASTM C 157-99) [16]. 4. Creep of concrete in compression (ASTM C 512-02) [17].

See Fig. 1.

IV. RESULTS AND DISCUSSION

A. Strength-density relationship The results of the 28-day dry density and compressive strength at different ages are shown in Table4. Examining Table 4 shows that increasing the P/B ratio had caused density and strength to decrease but with different rates. The 28-day compressive strength showed steeper reduction than density. The 10% increase in P/B ratio caused 5, and 2 percent decrease in compressive strength and density respectively. Meanwhile, increasing another 10% in the lightweight aggregate volume made the reduction in these values to continue until reaching 21, and 5 percent respectively. Using saturated aggregate, with its all internal voids filled with moisture, may cause the density not to change much when increasing aggregate volume. Also, internal curing offered by the saturated aggregate would enhance the characteristics of the interface zone and decrease microcracking. B. Shrinkage and creep deformations Table 5 shows the development of shrinkage strain with time for mixes M0, M10, and M20. It is clear that the shrinkage strain decreases 7% and 12% as the P/B ratio increases 10% and 20% respectively. Increasing Porcelinite aggregate volume had caused the decrease of binder volume and the increase of interface zone area.Both factors resulted in decreasing shrinkage strain through less volume change and better bond (higher restraining action). Al-Attar [18] concluded that all the measures which enhance bond between aggregate and cement paste, would reduce shrinkage strains. Fig. 2 displays the relationship of relative shrinkage (εsht / εshu) with time. This parameter could be used as an indication for shrinkage development rate. The three mixes showed almost the same rate till the age of 28 days. Later to that, mixes M0 and M10 remained showing the same rate, meanwhile, mix M20 showed a lower rate. This mix, M20, had also a lower ultimate shrinkage strain. Table 6 shows a comparison among mixes M0, M10, and M20 with respect to creep strain and specific creep (unit creep) at different loading times. The creep strain, at 364-day after loading, decreases 10% when the P/B ratio increases about 10% and about 25% when the P/B ratio increases 20%. Creep is a function of the volumetric content of cement paste in concrete; therefore, increasingthe lightweight aggregate volume, which has lower density, in mixes M10 and M20 would reduce the paste volume and hence cause creep strains to be smaller, but the relationship is not linear [19]. In addition to that, the difference between the modulus of elasticity of the LWA and the hydrated cement paste is small and according to Bremner and Holm [20] that elastically matched constituents would result in lower levels of stress at the interface zone and less microcracking and better bond. Specific creep (creep strain/unit stress) for the three mixes, as shown in Fig. 3, had the same trend in variation with age but with small differences.



This parameter is more indicative than creep strain because it is directly connected to applied stress and indirectly to strength level of concrete. Therefore, it could be concluded that, when connecting recorded strain with strength level, no significant difference is observed in creep behavior for the three mixes. C. Stress-strain Relationships Fig. 4 represents the stress-strain relationships for the three mixes in compression. The ultimate stresses reached were 33.7, 31.0, and 25.1 MPa for M0, M10, and M20 respectively. The recorded strain values at these ultimate stresses were 0.0034, 0.0032, and 0.0024 respectively. Increasing the P/B ratio caused the ultimate stress to decrease, meanwhile, the ultimate strain, associated with failure, remained almost constant. The three curves have a linear ascending part (up to approximately 80% of ultimate stress). This linearity is attributed, mainly, to the absence of early development of bond microcracking in the interface zone between the lightweight aggregate and the binder matrix [19]. The effect of different P/B ratios on the area under the stress-strain curve (which represents the toughness) is also shown in Fig. 3. This area becomes smaller and the descending part of the curve becomes less steep when the P/B ratio is increased, which indicates less ductile behavior [21].

V. CONCLUSIONS

1. Porcelinite rocks could be used to produce high performance lightweight concrete mixes. The 28-day dry density of such mixes had ranged between 1878 and 1978 kg/m3, meanwhile, the 28-day compressive strength had ranged between 34 and 45 MPa. 2. Increasing the volumetric content of lightweight aggregate by 10 and 20 percent had caused density and compressive strength to decrease but with different rates. Density was less affected by this change and that could be attributed to the absence of early development of bond microcracking in the interface zone and to using saturated aggregate. 3. Using higher Porcelinite to binder ratios had always negative effect on shrinkage of HPLC. Mix M20 (with P/B = 2.4 by volume) showed the lowest shrinkage magnitude and rate. 4. No significant decrease was observed in specific creep of the tested mixes when adopting higher P/B ratios.

VI. FURTHER NEEDED RESEARCH

1. In order to examine the found trend of variation in specific creep, lower and higher levels of strength should be achieved. In other words, lower and higher water to binder ratios could be adopted. 2. Examining shrinkage and creep for mixes produced by using all lightweight aggregate (i.e. for both fine and coarse aggregate).

REFERENCES

[1] F. O. Slate, A. H. Nilson, and L. Martinez, “Mechanical Properties of High Strength Lightweight Concrete” ACI Journal, vol. 83, pp. 606-613, July-Aug, 1986. [2] ACI Committee 213, “Guide for Structural Lightweight-Aggregate Concrete, ACI 213R-03”, ACI Manual of Concrete Practice, American Concrete Institute, Michigan, 38 pp., 2004 (on CD). [3] T. Faust, and G. Konig, “High Strength Lightweight-Aggregate Concrete” 2nd International PhD Symposium in Civil Engineering, Budapest, pp.1-8, 1998. [4] L. F. Khan, and M. Lopez, “Prestress Losses in High Performance Lightweight Concrete Pretensioned Bridge Girders” PCI Journal, pp. 84-94, Sep.-Oct. 2005. [5] J. S. Al-Sakini, “Behavior of High Performance Lightweight Aggregate Concrete” PhD. Thesis, University of Technology, Iraq, 2006. [6] S. Weber, and H. Reinhardt, “A Blend Aggregates to Support Curing of Concrete” Proceedings of International Symposium on Structural Lightweight Aggregate Concrete, Norway, pp. 662-671, 1996. [7] M. Lopez, L. F. Kahn, and K. E. Kurtis, “Effect of Internally Stored Water on Creep of High Performance Concrete” ACI Materials Journal, vol. 105, pp. 283-294, May-June 2008. [8] M. G. Alexander, “Aggregates and the Deformation Properties of Concrete” ACI Materials Journal, vol. 93, pp. 1-9, Nov.-Dec. 1996. [9] M. Lopez, “Creep and Shrinkage of High Performance Lightweight Concrete: a Multi-Scale Investigation” Doctoral Thesis Dissertation, Georgia Institute of Technology, Georgia, 2005. [10] ASTM Standard Specification for Portland Cement, C 150-02a, Annual Book of ASTM Standards, vol. 0401, Pennsylvania, 2003. [11] ASTM Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete, C 618-03, Annual Book of ASTM Standards, 0402, Pennsylvania, 2003. [12] ASTM Standard Specification for Chemical Admixtures for Concrete, C 494 /C 494M-99a, Annual Book of ASTM Standards, vol. 0402, Pennsylvania, 2003. [13] ACI Committee 211,”Standard Practice for Selecting Proportions for Structural Lightweight Concrete, ACI 211.2-98” ACI Manual of Concrete Practice, Michigan, 18 pp, 2004 (on CD). [14] ASTM Standard Test Method for Determining Density of Structural lightweight Concrete, C 567-00, Annual Book of ASTM Standards, vol. 0402, Pennsylvania, 2003. [15] ASTM Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens, C 39 /C 39M-01, Annual Book of ASTM Standards, vol. 0402, Pennsylvania, 2003. [16] ASTM Standard Test Method for Length Change of Hardened Hydraulic-Cement Mortar and Concrete, C157 /C 157M-99, Annual Book of ASTM Standards, vol. 0402, Pennsylvania, 2003. [17] ASTM Standard Test Method for Creep of Concrete in Compression, C 512-02, Annual Book of ASTM Standards, vol. 0402, Pennsylvania, 2003.



[18] T. S. Al-Attar, “Effect of Coarse Aggregate Characteristics on Drying Shrinkage of Concrete” Engineering and Technology Journal, University of Technology Press, Baghdad, vol. 26, pp.146-153, 2008. [19] A. M. Neville, Properties of Concrete. 4th ed. Longman, Essex, 844 pp., 1995. [20] W. Bremner, and T. A. Holm, “Elastic Compatibility and the Behavior of Concrete” ACI Journal, vol. 83, pp.244-250, 1986. [21] J. Newman, and P. Owens, “Properties of Lightweight Concrete” in Advanced Concrete Technology vol. 3 - Processes, edited by J. Newman, and B. S. Choo, Oxford, Elsevier, 2003.

Tareq S. Al-Attar was born in Baghdad, Iraq in 1960. He received his BSc in civil engineering in 1982 and his MSc in materials engineering in 1989. These degrees both were from the University of Baghdad, Iraq. In 2001, he received his PhD in materials engineering from the University of Technology, Iraq. At present, he is an assistant professor of civil engineering in the Building and Construction Engineering Department, University of Technology,

Iraq. His Research interests include time-dependent deformations of concrete, durability of concrete and high performance concrete. Dr. Al-Attar is a member of the Iraqi Union of Engineers since 1982, an affiliate member of the American Society of Civil Engineers, ASCE, since 2004, and a member of the American Concrete Institute, ACI, since 2005.

TABLE 1 PROPERTIES OF PORTLAND CEMENT AND METAKAOLIN

No Property OPC M

1 Oxide Content, %.

CaO 61 0.8 SiO2 20 57 Al2O3 5.7 36 Fe2O3 3 1.4 MgO 1.6 0.7 K2O 0.48 0.23 Na2O 0.11 0.03 SO3 2.3 0.03 TiO2 - 2.13

2 Loss on Ignition, LOI. 0.5 1.4 3 Fineness (Blaine), m2/kg. 312 1900 4 Specific Gravity. 3.15 3.11

5 Compressive Strength, MPa, at:

3 days 24 - 7 days 29 - 28 days 47 -

TABLE 2

PHYSICAL PROPERTIES OF PORCELINITE LIGHTWEIGHT AGRREGATE

No. Property Value

1 Sieve Analysis

Sieve Size, mm. % Passing 12.50 100 9.50 90 4.75 10 2.36 0

2 Specific Gravity. 1.49 3 Water Absorption, %. 35 4 Dry Rodded Unit Weight, kg/m3. 830

TABLE 3

MIX DETAILS

Mix

Mix Proportions, kg/m3.

P/B Ratio

by vol.

Slump, mm.

OPC M Sand P M0 506 44 500 520 2.00 102 M10 496 43 500 560 2.20 92 M20 482 42 500 598 2.40 86

TABLE 4

RESULTS OF DENSITY AND STRENGHT TESTS

Mix 28-day

dry density, kg/m3

Compressive strength , MPa at ages:

7 d 28 d 90 d 120 d M0 1978 28 43 58 60 M10 1930 25 41 55 57 M20 1878 20 34 45 46

TABLE 5

RESULTS OF SHRINKAGE TEST Mix M 0 M10 M20

Drying time, days.

εsht, × 10-6

εsht / εshu

εsht, × 10-6

εsht / εshu

εsht, × 10-6

εsht / εshu

1 42 0.08 38 0.08 34 0.07 7 104 0.19 96 0.19 83 0.17 14 111 0.20 101 0.20 91 0.19 28 175 0.32 159 0.31 139 0.29 56 240 0.44 204 0.40 175 0.36 91 334 0.61 292 0.57 271 0.60 154 430 0.78 390 0.77 339 0.70 182 463 0.84 426 0.84 379 0.78 210 498 0.91 452 0.89 393 0.81 280 530 0.96 502 0.98 437 0.90 364 550 1.00 510 1.00 485 1.00

TABLE 6

RESULTS OF CREEP TEST Mix M 0 M10 M20 Time after

loading, days.

εcreep, × 10-6

Specific creep,

10-

6/MPa

εcreep, × 10-6

Specific creep,

10-

6/MPa

εcreep, × 10-6

Specific creep,

10-

6/MPa 1 310 23.1 237 19.6 238 22.9 7 566 42.2 457 37.8 428 41.2 14 702 52.4 577 47.7 529 50.9 28 870 64.9 730 60.3 652 62.7 56 1079 80.5 923 76.3 805 77.4 91 1255 93.7 1088 89.9 933 89.7 154 1477 110.2 1299 107.4 1094 105.2 182 1556 116.1 1375 113.6 1151 110.7 210 1626 121.3 1443 119.3 1203 115.7 280 1778 134.0 1591 133.0 1312 128.4 364 1834 136.9 1650 136.4 1380 132.7

International Journal of Civil & Environmental Engineering IJCEE

Fig. 1. Creep test rigs.

Fig.2. Development of relative shrinkage (εsht / εshu) with time for mixes MM10, and M20.

Fig. 3. Development of specific creep with loading time for mixes Mand M20.

International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol: 11 No

113206-7575 IJCEE-IJENS © December 2011 IJENS

) with time for mixes M0,

with loading time for mixes M0, M10,

Fig. 4. Stress-strain relationships for mixes M

IJENS Vol: 11 No: 06 58

I J E N S

strain relationships for mixes M0, M10, and M20.

Effect of Aggregate to Binder Ratio on Shrinkage and Creep ...American corporation built concrete...

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