STRUCTURAL BEHAVIOR OF GEOPOLYMER CONCRETE COLUMN DUE TO CONCENTRIC AND CYCLIC AXIAL- LATERAL LOADS

• Main Author: Herwani
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/57054
• Institution: Institut Teknologi Bandung

Geopolymer concrete is a concrete composed of coarse and fine aggregates without a Portland cement (OPC) binder. Instead, a binder from a material that contains a lot of silica and alumina is used, namely fly ash. This concrete has advantages such as high compressive strength, good durability, resistance to corrosion attack, low shrinkage, high bond strength and environmentally friendly. In the field of construction materials, the focus of research conducted on geopolymer concrete is more emphasized on its application as precast concrete for beams, columns and other constructions that are directly affected by the external environment. However, it is very rare to test the cyclic behavior of geopolymer concrete structural elements that represent earthquake loads. The cyclic behavior of geopolymer concrete column has not been understood specifically and in more detail. While the application of geopolymer concrete for structural elements is very likely to be applied to buildings in areas with a high risk of earthquakes. Therefore, it is very necessary to understand the behavior of geopolymer concrete structures due to cyclic lateral loads which represent earthquake loads. This dissertation aims to study and understand the structural behavior of geopolymer concrete column elements due to concentric and lateral cyclic axial loads, including structural ductility, load bearing capacity, failure pattern, energy dissipation and hysteresis behavior. The research consisted of three main phases, namely testing of mechanical properties, testing of column structural elements against concentric axial loads and testing of column structural elements against cyclic axial-lateral loads. Phase I is testing the mechanical properties of geopolymer concrete to determine the compressive strength, modulus of elasticity, splitting tensile strength and bond strength of concrete. The test object is a concrete cylinder with a height of 200 mm and a diameter of 100 mm based on ASTM C39, while the bond strength test uses the direct tensile strength method (Pull out Test) according to ASTM C234. Phase II is testing of column structural elements due to concentric axial loads carried out on square columns measuring 170 x 170 mm high 480 mm with variable compressive strength of concrete and spacing of stirrup reinforcement. The test objects were made of 12 pieces consisting of 3 plain concrete columns and 9 reinforced concrete columns. The compressive strength of the concrete used was 26.2, 30.45 and 37.87 MPa, while the spacing of the stirrup reinforcement was determined to be 30, 50 and 70 mm. For longitudinal reinforcement, 4 bars of 10 mm diameter deformed steel were used, while 8 mm diameter undeformed steel bars were used as stirrup reinforcement. Phase III is testing column structure elements against cyclic axial-lateral loads. The test was carried out on 5 square columns measuring 260x260 mm with a height of 1500 mm consisting of 4 geopolymer concrete columns and 1 conventional concrete column as a comparison. Both ends of the column were given a pile cap size of 1100x600x400 mm, so that the total height of the test object was 2300 mm. For longitudinal reinforcement, 8 bars of 13 mm diameter deformed steel were used, while 10 mm diameter deformed steel was used as stirrups. The variables used are stirrup distance and axial load level. The hoop spacing is 50, 70, and 90 mm while the axial load levels are 0.3Po and 0.5Po. The results of the mechanical properties test show that the characteristics of geopolymer concrete are similar to conventional concrete. Only the value of the Poisson ratio of geopolymer concrete is greater than that of conventional concrete. The empirical formula used to determine the modulus of elasticity in conventional concrete can be used for geopolymer concrete. Likewise, the results of column testing due to axial load, geopolymer concrete column behavior is similar to conventional concrete columns. When referring to the results of column testing against concentric axial loads, the required transverse reinforcement area is only half of the minimum area specified in SNI/ACI. This shows that the minimum required area has anticipated the possibility of load eccentricities and lateral loads to a certain extent. This behavior can be seen from the results of column testing against cyclic lateral-axial loads, where the column with the minimum required transverse reinforcement area is still able to withstand the axial load level P < 0.3Po with a ductility of 2.5%. Overall, the results of the research on geopolymer concrete structural elements due to concentric axial and cyclic lateral axial loads show similar behavior to conventional concrete column elements. This confirms that geopolymer concrete has the same opportunities as conventional concrete for applications in earthquake-resistant structural elements. From the research data, several mathematical formulations for geopolymer concrete materials and structures have been developed which are the latest in research, including the formulation of concrete tensile strength, bond strength, and expansion length, minimum area of transverse reinforcement and compressive strength of confined concrete. In addition, several graphs were also made, including the relationship between the reinforcement diameter versus the expansion length and the axial load level versus the transverse reinforcement area.