ALWA MATERIAL DEVELOPMENT AS INTERNAL CURING AGENT ON HIGH PERFORMANCE CONCRETE

• Main Author: Kania Kurniawati, Euis
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/57069
• Institution: Institut Teknologi Bandung

High-Performance Concrete (HPC) commonly uses a low water-cement ratio (w/c). The low water-cement ratio (w/c) mostly has low water content and high cement content. It causes a less than interfacial transition zone (ITZ) so that additional mineral pozzolan is required, such as Silica Fume (S.F.), Slag and, Fly Ash (F.A.). The pozzolanic material increases the amount of paste in concrete and lead to a higher shrinkage. The shrinkage of the concrete itself is one of the consequences of moisture loss during the hardening process. Shrinkage affects cracking at an early age (early age cracking) which will cause cracks due to loading and others so that an effective cured process is needed and keep the concrete moist, so it prevents potential shrinkage in the concrete. Conventionally, some of this additional water has been provided by external curing techniques such as immersion, fogging, spraying, and the application of wet burlap. However, in a high-strength performance concrete, the capillary porosity becomes severed during the first few days of hydration, which causes external water to only penetrate a few mm into the concrete from the curing applied. So that external curing is no longer adequate for concrete with early age hardening. A direct curing method was needed from within the concrete itself, often called internal curing (IC). The research begins with an investigation of the soil base material, testing the material properties of Artificial Lightweight Aggregate (ALWA) in accordance with the ASTM C1761M-13b (Standard Specification for Lightweight Aggregate for Internal Curing of Concrete) standard, among others physical characteristics of the material (sludge content, gradation of aggregates, Bulk Density, Absorption, Desorption) and chemical characteristics (Organic Impurities, staining, and Loss of Ignition, LOI). The development of IC materials will be applied to high-quality performance concrete with low w / c variations of w / c 0,3, 0,35, and 0.4, to test some of the mechanical properties of the HPC concrete, which include compressive elastic modulus and flexural strength. Furthermore, other properties of durability concrete also have been tested, such as autogenous shrinkage potential, drying shrinkage, and the effect of concrete mixture to cracks due to variation in case of an autogenous and drying shrinkage occurred at the same time under restrained condition also has been tested. In addition, other observations were tested by SEM and XRD. It is expected that the microstructure analysis and physical analysis results supported the results of concrete mechanical properties and the concrete behavior against shrinkage. So the result will be identified what is affecting the improvement or decrease in the properties of concrete, either due to an increase in hydration of the concrete, improvement of the ITZ area, and others. The results had shown that the use of ALWA as an internal curing material quietly effective where the concrete is given better mechanical properties when the compressive strength and modulus of elasticity were higher than normal conditions, and the modulus of rupture met the minimum rupture modulus standard according to ACI. ALWA concrete was more resistant to shrinkage, where the test results showed decreases in autogenous and drying shrinkage and increases in crack age which indicates a reduction in concrete tensile stress on restrained condition. The study of mechanical properties and shrinkage resistance was also validated by the results of microstructural and physical testing, including the results of TGA DTA analysis, XRD analysis, and SEM-EDS analysis. The result showed that more CSH compounds were formed, which indicated the first and second hydration reactions more completely occurred so that the ITZ structure was denser. Thus the use of ALWA in concrete can increase the ability of HPC concrete both in terms of mechanical properties and behavior in terms of shrinkage. So that concrete can be classified into concrete with low shrinkage (low shrinkage concrete).