FAILURE MODE AND STRENGTH CHARACTERISTICS OF NON-GRADED COARSE AGGREGATE CONCRETE BEAMS

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 7, Issue 5, September-October 2016, pp , Article ID: IJCIET_07_05_049 Available online at ISSN Print: and ISSN Online: IAEME Publication FAILURE MODE AND STRENGTH CHARACTERISTICS OF NON-GRADED COARSE AGGREGATE CONCRETE BEAMS Haider Amer Mushatat Al-Mustansirya University, College of Engineering Civil Engineering Department, Baghdad, Iraq. ABSTRACT This paper is devoted to investigate experimentally the variation of mechanical properties of concrete as a result of using one grade of crushed and rounded gravels gradient in conventional concrete mix instead of well graded gravel, in addition to its effect on structural behavior of reinforced concrete beams. The experimental work includes investigation of 30 cube, 30 cylinder and 30 prisms specimens to evaluate compressive strength, modulus of elasticity and modulus of rupture for concrete. While the structural behavior of reinforced concrete beams has been studied through casting and testing of ten (180 *200 * 1100) mm beam specimens. This work concluded that the failure mode has been changed from flexural to shear failure, failure and cracking loads was also affected adversely by using one gradient of gravel and the ductility and stiffness are decreased when using one gradient of gravel instead of well graded gravel. Key words: Compressive strength, flexural strength, shears failure, deflection, ductility, stiffness. Cite this Article: Failure Mode and Strength Characteristics of Non-Graded Coarse Aggregate Concrete Beams. International Journal of Civil Engineering and Technology, 7(5), 2016, pp INTRODUCTION The structural behavior of reinforced concrete members depends greatly on the durability of concrete. The high durability concrete resist stresses better than the concrete with low durability [Behrouz M. (2006)] (1), [Gagan and Agam (2015)] (2), and [Sagar P. and H.B. Balakrishna (2014)] (3). The durability of concrete depends mainly on the grading of aggregates (4), maximum size of aggregates (5), sulfate ratio in aggregate (6), and physical and chemical properties of cement (7). This study focuses on the impact of the using one grade of crushed and rounded gravels gradient on the concrete properties as well as its impact on the structural behavior of concrete beams. 2. EXPERIMENTAL WORK The constituent material properties required for casting ten reinforced normal strength concrete (NSC) beams of dimension (1100 mm length, 180 mm width, and 200 mm height) are listed below: editor@iaeme.com

2 Failure Mode and Strength Characteristics of Non-Graded Coarse Aggregate Concrete Beams Pavement Thickness 2.1. Cement Ordinary Portland Cement (OPC), (Type I) was used for all mixes of NSC. To avoid any differences between various batches, the whole quantity was brought and stored in a dry place. The chemical composition and physical properties of used cement are shown in Tables (1) and (2) respectively. The results confirm to the Iraqi Specifications No.5/1984 (8). Table 1 Chemical Composition and Main Compounds of Cement Oxide composition Abbreviation Content% Limits of Iraqi specification No.5/1984 Lime CaO _ Silica SiO _ Alumina Al 2 O _ Iron Oxide Fe 2 O _ Sulfate SO % Magnesia MgO % Loss on ignition L.O.I % Insoluble residue I.R % Lime saturation factor L.S.F Main Compounds (Bogue s equations) Tricalcium Aluminate C3A 9.37 Table 2 Physical properties of the cement used in this study Physical properties Test results Limit of Iraq specification No.5/1984 Specific surface area, (Blaine method),cm 2 /gm Soundness (LeChatelier Method) 1 10 mm Setting time (vicat s apparatus) Initial setting, hrs: min Final setting,hrs :min Compressive strength 3days, MPa 7days, MPa 2:30 5:10 0:45 10: Fine Aggregate A natural sand of 4.75 mm maximum size is used as fine aggregate for (NSC). The obtained results indicate that the fine aggregate grading and the sulfate content are within the requirements of the Iraqi specificationno.45/1984 (9). Sand grading and physical properties are shown in Tables (3) and (4) respectively editor@iaeme.com

3 Haider Amer Mushatat Sieve size Table 3 Grading of Fine Aggregate (sand) Cumulative Passing% Limits of Iraqi specification No.45/1984, zone Table 4 Physical Properties of Fine Aggregate Physical properties Test results Limits of Iraqi specification No.45/1984 Specific gravity Sulfate content % Absorption 0.74% Coarse Aggregate A nominal (5-40), crushed and rounded gravel was used in concrete mix. The gravel was washed, and then stored in a saturated dry surface condition before using. The grading of the coarse aggregate is shown in Table (5) and Table (6). The obtained results indicate that the coarse aggregate grading is within the requirements of the standards Iraqi Specification No. 45/1984 (9). Sieve size Table 5 Grading of Rounded Coarse Aggregate %Coarse Aggregate %Passing Iraqi specification No. 45/1984, Nominal size(5-40) 37.5mm mm mm mm mm mm editor@iaeme.com

4 Failure Mode and Strength Characteristics of Non-Graded Coarse Aggregate Concrete Beams Pavement Thickness Table 6 Grading of Crushed Coarse Aggregate Sieve size %Coarse Aggregate %Passing Iraqi specification No. 45/1984, Nominal size(5-40) 37.5mm mm mm mm mm mm Steel Reinforcement Ten concrete beams are tested in this study. The reinforcement consists of four deformed bars, 2Ø10mm as main tension steel reinforcement and 2Ø10 mm as main compression longitudinal reinforcement, also Ø6 mm smooth mild steel bars was used as stirrups reinforcement at 60 mm center to center. Three (500 mm length) specimens prepared from each size of the steel bars to determine their tensile properties according to ASTM C370-05a, The test results indicate that the adopted steel reinforcing bars confirm to ASTM A (10), as shown in Table (7). Nominal Diameter Table 7 Specifications and Test Results of Steel Reinforcement Measured Diameter Yield Strength (fy) (MPa) Ultimate Tensile Strength(fu) (MPa) CONCRETE MIXES Normal strength concrete mix is designed according to ACI Code 318M-11 (11), mixture details are given in Table (8). The reinforced concrete beams with control specimens per each mix have been achieved. Nongraded crushed gravel and rounded gravel used in this mix editor@iaeme.com

5 Haider Amer Mushatat Table 8 Designation and Properties of concrete Designation Size of the Gravel used in Concrete mix Gravel Type Cement (kg/m 3 ) Sand (kg/m 3 ) Gravel (kg/m 3 ) W/C B*(5-40) size(5-40) B37 37 B20 20 B14 14 B10 10 BC**(5-40) size(5-40) BC37 37 BC20 20 BC14 14 BC10 10 Rounded Crushed *B refer to the concrete beam **BC refer to the crushed gravel in concrete beam 4. MECHANICAL PROPERTIES OF CONCRETE A series of tests were carried out using (150*300) mm concrete cylinders to determine the compressive strength accordance with ASTM- C39/C39M-05 (12) and modulus of elasticity accordance with ASTM C (13). Also (150mm) cubes were tested to estimate the compressive strength accordance with BS1881-Part 116 (14).The modulus of rupture was carried out using (100*100*500) mm prisms accordance withastm-c78-02 (15), The mechanical properties are illustrated in Table (9). Table 9 Concrete Test Results Designation Average Compressive Strength of Cylinder( f c ') (MPa) Average Compressive Strength of Cube(f cu ) (MPa) Average Flexural Tensile Strength(f r)(m Pa) Modulus of elasticity (MPa) B(5-40) BC(5-40) B B B B BC BC BC BC editor@iaeme.com

6 Failure Mode and Strength Characteristics of Non-Graded Coarse Aggregate Concrete Beams Pavement Thickness 5. FAILURE MODE In the early stages of loading, the beams behave elasticity up to the appearance of the first crack, this period is the first linear stages, in which the specimen restores to the primary position when lifting the load. After the appearance of first crack, the cracks begin to increase in length towards the compression zone of the specimen till yielding of the steel bars, this stage is also linear but the beam at this stage does not return to the normal position before loading because of loss of bonding between steel and concrete. After yielding of steel bars, the deflections begin to get more rapidly and the crack width begin to increase clearly and no appearance of new cracks up to failure of tested specimens. It is noticed that the reference beams with full gradients of rounded and crushed aggregate failed by flexure, while the other beams failed by diagonal shear. In other word, the loss of gradients of coarse aggregate lead to transform the failure mode from well controlled failure (flexure) to another type of failure (shear) which is sudden and uncontrolled mode, see Figure (1) to Figure (10). Figure 1 Failure Pattern of Beam B (5-40) Figure 6 Failure Pattern of Beam BC (5-40) Figure 2 Failure Pattern of Beam B37 Figure 7 Failure Pattern of Beam BC37 Figure 3 Failure Pattern of Beam B20 Figure 8 Failure Pattern of Beam BC editor@iaeme.com

7 Haider Amer Mushatat Figure 4 Failure Pattern of Beam B14 Figure 9 Failure Pattern of Beam BC14 Figure 5 Failure Pattern of Beam B10 Figure 10 Failure Pattern of Beam BC10 6. ULTIMATE CAPACITY In general, the using of one aggregate size adversely affect the maximum ultimate load of reinforced concrete beams specimens, the reason is that the spacing between gravels are filled with cement mortar which is weaker than the gravels. It is observed that the amount of decrease in the ultimate capacity is inversely proportional to the used aggregate size. In other word, whenever the used size is large the amount of decreasing in the ultimate capacity is less. The above conclusion can be seen clearly when comparing the specimens (B37, B20, B14 and B10) with the reference specimen's B (5-40) in rounded gravel, since the percentage of decreasing is (5.6, 11.36, 28.4 and 33) % respectively. The same manner can be seen in case of crushed gravel, the amount of strength reduction is about (6.6, 11.4, 19 and 30.5) % in beams (BC37, BC20, BC14 and BC10) respectively in comparison with reference specimen BC (5-40). See Table (10). Table 10 Ultimate Loading Capacity Ultimate load (kn) % of decreasing B (5-40) 88 - B B B B BC (5-40) BC BC BC BC editor@iaeme.com

8 Failure Mode and Strength Characteristics of Non-Graded Coarse Aggregate Concrete Beams Pavement Thickness 7. CRACKING CAPACITY The cracking capacity (first crack load) may be defined as the stage of loading when the tensile stresses in the beam reaches the modulus of rupture (fr). In this study, the appearance of first cracking load is affected clearly by using one aggregate size. This behavior can be seen in Table (11), which the percentage of decreasing in appearance of cracking load is (23.3, 33.3, 43.3 and 58.3) for beams (B37, B20, B14 and B10) respectively in compression with reference specimen's B (5-40) for rounded aggregate. In crushed aggregate beams the percentage of decreasing in cracking load is also affected when using one aggregate size but the ratio of decreasing is less than the ratio in rounded aggregate beams, the percentage of decreasing reached to (9.4, 28.12, and 43.75) in beams (BC37, BC20, BC14 and BC10) respectively in comparison with reference specimen BC (5-40). The reduction of cracking capacity is attributed to decreasing the neutral axis depth as a result of decreasing the compressive strength. Also, the amount of reduction of cracking capacity increased with using smaller aggregate size. Table 11 Cracking Capacity cracking load (kn) % of decreasing B (5-40) 30 - B B B B BC (5-40) 32 - BC BC BC BC DUCTILITY OF TESTED SPECIMENS Ductility is measure of how much deformation or strain a member can withstand before failure, it is the ratio of the ultimate deflection to the yielding deflection as indicated in Table (12), it is clear that the effect of using one gradient of coarse aggregate affect to some extent on decreasing the ductility of tested specimens, and the amount of reduction increase with decreasing the size of grade used. Table 12 Ductility and Deflection Characteristics Max. deflection Yield deflection Ductility % of decreasing B (5-40) B B B B BC (5-40) BC editor@iaeme.com

9 Haider Amer Mushatat BC BC BC STIFFNESS OF TESTED SPECIMENS Stiffness is the rigidity of an object, the extent to which it resists deformation in reference to an applied force. The stiffness of the body is a measure of the resistance offered by an elastic body to deformation; the stiffness is calculated from the ratio between the force and the produced deflection. From the table (13), it turns out that the amount of stiffness decreased when using one gradient of coarse aggregate, and the amount of reduction increased as the used aggregate size is decreased, which the specimens fail with low strength and large displacement. 10. CONCLUSION Max. deflection Table 13 Stiffness Characteristics Ultimate load (kn) Stiffness (N.mm) % 0f decreasing B (5-40) B B B B BC (5-40) BC BC BC BC The failure mode is affected by using one gradient of gravel from flexural failure to shear failure. Decreasing the ultimate capacity of beams is a result of using one gradient of gravel in concrete mixture. The cracking capacity is decreased when using one gradient of gravel in concrete mixture. The ductility of beams decreases when using one gradient of gravel in concrete mixture. One gradient of gravel specimens fails with low strength and large displacement, i.e. the stiffness of members is decreased. The mechanical properties (compressive strength, tensile strength, modulus of elasticity and modulus of rupture) of non-graded aggregate concrete are decreased. REFERENCE [1] Behrouz P.,"The Effect of Sulfate Solution on the Behavior of Reinforced Concrete Beams", Electronic Journal of Structural Engineering, Vol. 6, pp.49-55, [2] Gagan and Agam, " Flexural Behavior of Reinforced Recycled Concrete Beams: A Review", International Journal of Research in Engineering and Technology", Vol. 4, Issue 1, pp. 1-6, February, editor@iaeme.com

10 Failure Mode and Strength Characteristics of Non-Graded Coarse Aggregate Concrete Beams Pavement Thickness [3] Saggar, P. and Balakrishna H. B, " Flexural Behavior of Reinforced Concrete Beams Replacing GGBS as Cement and Slag Sand as Fine Aggregate", International Journal of Civil and Structural Engineering Research, Vol. 2, Issue 1, pp.(66-75), April, [4] Okoukwo, V. O. and Arinze E., " Effects of Aggregate Gradation on the Properties of Concrete Made from Granite Chippings", International Journal of Advancements in Research and Technology, Vol. 4, Issue 12, pp 17-20, December, [5] Rozalija, K. and David D.," Effect of Aggregate Type, Size and Content on Concrete Strength and Fracture Energy". The Reinforced Concrete Research Council, Project 56, University of Kansas, June, [6] Zainab, H. A. A., "Effect of Sulfate in Sand on Some Mechanical Properties of Nano Metakaolin Normal Concrete", Journal of Babylon University, Engineering Sciences, Vol. 24, No. 1, pp , [7] Humphrey, D. and Isaac, B.," Quality of Type I Portland Cement from Ghana and UK", Civil and Environmental Research, Vol. 7, No.1, pp , [8] IQS No.5/1984, "Portland Cement," Central Agency for Standardization and Quality Control, Planning Council, Baghdad, IRAQ, (in Arabic). [9] IQS No.45/1984, Iraqi Specification, "Aggregate from Natural Sources for Concrete and Construction", Central Agency for Standardization and Quality Control, Baghdad, (in Arabic) [10] ASTM A "Standard Specification for Deformed and Plain billet-steel bars for Concrete Reinforcement", Annual Book of American Society for Testing and Material Standards, Vol , [11] ACI Code 318M-11 Building Code Requirements for Structural Concrete and Commentary.American Concrete Institute. [12] ASTM C39/C39M-05, "Standard Test Method for Compressive Strength of Cylindrical Concrete," Annual Book of ASTM Standards, Vol Concrete and Aggregates, West Conshohocken, PA, United States, 2005, 7pp. [13] ASTM C Standard Test Method for Static Modulus of Elasticity and Pisson s Ratio of Concrete in Compression. Philadelphia: American Society for Testing. [14] BS 1881-Part 116: 1983," Method for determination of compressive strength of concrete cubes," British Standards Institute BSI, London, 2000,11pp. [15] ASTM C78-02,"Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Fourth-Point Loading),"Annual Book of ASTM Standards, Vol Concrete and Aggregates, West Conshohocken, PA, United States, 2002, 3pp. [16] Pinal C. Khergamwala, Dr. Jagbir Singh and Dr. Rajesh Kumar, Effect of Recycled Coarse Aggregates on Characteristic Strength of Different Grades of Concrete. International Journal of Civil Engineering and Technology (IJCIET), 4(6),2014, pp [17] M.K.Thangamanibindhu and Dr.D.S.Ramachandra Murthy, Flexural Behaviour of Reinforced Geopolymer Concrete Beams Partially Replaced with Recycled Coarse Aggregates. International Journal of Civil Engineering and Technology (IJCIET), 6(7), 2015, pp editor@iaeme.com