Effects of Aggregate Type, Size, and Content on Concrete Strength
CHAPTER ONE
OBJECT AND SCOPE
The purpose of this research is to compare the compressive strength, flexural strength, and fracture energy of normal and high-strength concretes with different aggregate types, sizes, and contents.
Compressive strengths range from 25 MPa (3,670 psi) to 97 MPa (13,970 psi). Fifteen batches (5 normal-strength concrete and 10 high-strength concrete) of 9 specimens each were tested. Some data cannot be used due to errors during testing. The results of 45 compression, 45 flexural, and 42 fracture energy tests are reported.
CHAPTER TWO
EXPERIMENTAL WORK
To study the effects of coarse aggregate type, size, and content on the behavior of concrete, prismatic specimens were tested in compression, in flexure using center-point loading, and a three-point bending test on notched beams. The concrete mixtures incorporated either basalt or crushed limestone, aggregate sizes of 12 mm (!12 in.) or 19 mm (Y. in.), and coarse aggregate contents with aggregate volume factors (ACI 211.1-91) of0.75 and 0.67. Water-to-cementitious material ratios ranged from 0.24 to 0.50.
Type I portland cement, silica fume, and fly ash were used in the concrete mixtures. The dry, compacted silica fume (Master Builders MB-SF) contained 92 percent Si02, 0.45 percent Nap, 0.36 percent S03, 0.10 percent Cl, and 0.52 percent loss on ignition. The Class C fly ash, supplied by Flinthills Fly Ash, contained 34 percent Si02, 29 percent CaO, 20 percent AI,03, 7 percent MgO, 4 percent Fe20 3 , and 3 percent S03 •
The fme aggregate was Kansas river sand with a fineness modulus= 2.60; bulk specific gravity (saturated surface dry)= 2.62; and absorption (dry)= 0.5 percent. The sand passed through a No. 4 sieve prior to use.
The 12 mm (Y, in.) and 19 mm (:Y. in.) maximum size basalt had a bulk specific gravity (saturated surface dry)= 2.64; and absorption (dry)= 0.4 percent. The unit weights (saturated surface dry) for the 12 mm (!12 in.) and 19 mm (:Y. in.) maximum size aggregates were 1480 kg/m3 (92.4lb/ff) and 1512 kg/m3 (94.4lb/ff), respectively. The 12 mm (!12 in.) maximum size crushed limestone had a bulk specific gravity (saturated surface dry)= 2.58; and absorption (dry)= 2.7 percent. The unit weight (saturated surface dry) for the 12 mm maximum size aggregate was 1450 kg/m3 (90.5 lb/ft3).
The water reducer used in the study was a Type A normal-range water reducer
(Master Builders Polyheed 997). The admixture had a specific gravity of 1.27 and contained 4 7 percent solids by weight. It was used at the rate of 460 ml per 100 kg of cementitious material (7 oz/cwt) for the high-strength test specimens. The high-range water reducer (HRWR) used was a calcium naphthalene sulfonate condensate-based material (Master Builders Rheobuild 1000). The HR. WR had a specific gravity of 1.20 and contained 40 percent solids by weight. The quantity of HR. WR used varied with each mixture because it was added until the desired workability was attained.
Mixtures were proportioned to limit the number of variables in the study. Cement replacement with 10 percent and 5 percent by weight of silica fume and fly ash, respectively, was kept constant in the high-strength mixtures, as was the total cementitious material content. The water-to-cementitious material ratio varied between 0.24-0.28 for the high-strength mixtures and was kept constant at 0.50 for the normal-strength mixtures. Mixture designs are given in Tables 2.1 and 2.2 for S! and customary units, respectively.
CHAPTER THREE
RESULTS
This chapter describes the results of the compression, flexure, and fracture energy tests. An evaluation of these tests will be presented in Chapter 4. The purpose of these tests is two-fold: (I) to determine the effects of aggregate type, size, and content on the behavior of normal and high-strength concrete, and (2) to determine the relationships between compressive strength, flexural strength, and fracture energy.
CHAPTER FOUR
EVALUATION
In this chapter, the results of the compression, flexure, and fracture energy tests discussed in the previous chapter are compared to previous research on the effects of aggregate type, size, and content for normal and high-strength concrete.
CHAPTER FIVE
SUMMARY AND CONCLUSIONS
SUMMARY
The purpose of this investigation is two-fold: (I) to determine the effects of aggregate type, size, and content on the compressive strength, flexural strength, and fracture energy of normal and high-strength concrete, and (2) to determine the relationships between these three measures of materials performance.
The concrete in this study incorporates either crushed basalt or limestone coarse aggregate with sizes of 12 mm (Y, in.) or 19 mm (%in.), and coarse aggregate contents with aggregate volume factors (ACI 211.1-91) of 0.67 or 0.75. Water-to-cementitious materials ratios range from 0.24 to 0.50. Compressive strengths range from 25 MPa to 97 MPa (3,670 psi to 13,970 psi).
Fifteen batches (5 normal-strength concrete and 10 high-strength concrete) of 9 specimens each were tested (except for HL-12h.l where only 6 specimens were tested). The results of 45 compression, 45 flexural, and 42 fracture energy tests are reported. Normal-strength concrete was tested at an age of 5 days and high-strength concrete was tested at ages of 94 to 164 days. Specimens were tested in compression and flexural using a 180,000 kg (400,000 lb) capacity hydraulic testing machine. Fracture energy tests were performed using an MTS closed-loop servo-hydraulic testing system.
CONCLUSIONS
The following conclusions are based on the findings for the materials used and tests performed in this study:
- High-strength concrete containing basalt produces slightly higher compressive strengths than high-strength concrete containing limestone, while normal-strength concrete containing basalt yields slightly lower compressive strengths than normal-strength concrete containing limestone.
- The compressive strength of both normal and high-strength concrete is little affected by aggregate size.
- High-strength concrete containing basalt and normal-strength concrete containing basalt or limestone yield higher compressive strengths with higher coarse aggregate contents than with lower coarse aggregate contents. The compressive strength of high-strength concrete containing limestone is not affected by aggregate content.
- High-strength concrete ~ containing basalt yields higher flexural strengths than concrete with similar compressive strength containing limestone. The flexural strength of high-strength concrete containing limestone is limited by the strength of the rock and the matrix. The flexural strength of high-strength concrete containing basalt is controlled by the strength of the rock and the interfacial strength at the matrix-aggregate interface. The flexural strength of normal-strength concrete containing the basalt or limestone used in this study is not affected by aggregate type, and is limited by the matrix strength and the strength of the interfacial transition zone.
- The flexural strength of normal and high-strength concrete is not affected by aggregate size.
- Normal and high-strength concretes containing basalt yield higher flexural strengths with higher coarse aggregate contents than with lower coarse aggregate contents.
FUTURE WORK
Although this study provides insight into the effects of aggregate type, size, and content in normal and high-strength concrete, a number of important questions cannot be answered with the available data. Of particular interest are the effects of aggregate size on the compressive strength, flexural strength, and fracture energy of concrete containing limestone. Tests need to be conducted to determine if differences in aggregate size affect concrete containing limestone as it affects concrete containing basalt.
The test results analyzed in this study are for concrete compressive strengths ranging from 25 to 30 MPa (3,670 to 4,430 psi) and from 62 to 96 MPa (9.070 to 13,970 psi). To obtain a complete understanding of the effects of aggregate type, size, and content, tests are required for compressive strengths spanning between the strength ranges, and also at later test ages for normal-strength concretes and earlier test ages for high-strength concretes.
Another aspect of the current study that needs further examination is the relative influence of ( 1) a larger maximum aggregate size and (2) a much lower coarse aggregate content for both normal and high-strength concretes.
Finally, a microscopic analysis of the concrete matrix and interfacial transition zone is needed to develop a complete understanding of the effects of aggregate on concrete. Only through a full understanding of the response of concrete under general loading can the behavior of this important construction material be understood.
REFERENCES
- ACI Committee 211. (1991) “Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete (ACI 211.1-91),” ACI Manual of Concrete Practice, 1997 Edition, Part I, Farmington Hills, MI.
- ACI Committee 363. (1992) “State-of-the-Art Report on High-Strength Concrete (ACI 363R-92),” ACI Manual of Concrete Practice, 1997 Edition, Part I, Farmington Hills, MI.
- Bayasi, Z. and Zhou, J. (1993) “Properties of Silica Fwne Concrete and Mortar,” ACI Materials Journal, V. 90, No.4, July-August, pp. 349-356.
- Bentur, A. and Mindess, S. (1986) “The Effect of Concrete Strength on Crack Patterns,” Cement and Concrete Research, V. 16, No. I, January, pp. 59-66.
- Bloem, D. L. and Gaynor, R. D. (1963) “Effects of Aggregate Properties on Strength of Concrete,” ACI Journal, Proceedings V. 60, No. 10, October, pp. 1429-1456.
- Carrasquillo, R. L., Nilson, A. H., and Slate, F. 0. (1981) “Properties of High-Strength Concrete Subject to Short-Term Loads,” ACI Journal, Proceedings V. 78, No.3, May-June, pp. 171-178.
- Carrasquillo, R. L., Slate, F. 0., and Nilson, A. H. (1981) “Microcracking and Behavior of High-Strength Concrete Subject to Short-Term Loading,” ACI Journal, Proceedings V. 78, No.3, May-June, pp. 179-186.
- Cook, J. E. (1989) “I 0,000 psi Concrete,” Concrete International, October, pp. 67-7 5.
- Cordon, W. A. and Gillespie, H. A. (1963) “Variables in Concrete Aggregates and Portland Cement Paste Which Influence the Strength of Concrete,” ACI Journal, Proceedings V. 60, No.8, August, pp. 1029-1052.
