An integrated microstructural-nanomechanical-chemical approach to examine material-specific characteristics of cementitious interphase regions

Abstract

Abstract:Effective properties and structural performance of cementitious mixtures are substantially governed by the quality of the interphase region because it acts as a bridge transferring forces between aggregates and a binding matrix and is generally susceptible to damage. As alternative binding agents like alkali-activated precursors have obtained substantial attention in recent years, there is a growing need for fundamental knowledge to uncover interphase formation ACCEPTED MANUSCRIPTA C C E P T E D M A N U S C R I P T mechanisms. In this paper, two different types of binding materials, i.e., fly ash-based geopolymer and ordinary portland cement, were mixed with limestone aggregate to examine and compare the microstructures and nanomechanical properties of interphase region. To this end, microstructural characteristics using scanning microscopies, nanomechanical properties by nanoindentation tests, and spatial mapping of chemical contents based on the energy dispersive spectroscopy were integrated to identify and investigate the interphase region formed by the case-specific interactions between the matrix materials and limestone. The integrated microstructural-nanomechanicalchemical approach was effective to better understand links between material-specific properties of cementing phases. More specifically, the fly ash-based geopolymer paste was usually well bonded to the aggregate surface with a rich formation of N-A-S-H gel, while interfacial debonding was often observed between aggregate surface and paste in ordinary portland cement concrete. However, when a good bonding between aggregate and paste is formed, interphase region in PCC didn't show any considerable difference in nanomechanical properties compared to the bulk paste. ACCEPTED MANUSCRIPT A C C E P T E D M A N U S C R I P T An Integrated Microstructural-Nanomechanical-Chemical Approach to Examine MaterialSpecific Characteristics of Cementitious Interphase Regions Abstract:Effective properties and structural performance of cementitious mixtures are substantially governed by the quality of the interphase region because it acts as a bridge transferring forces between aggregates and a binding matrix and is generally susceptible to damage. As alternative binding agents like alkali-activated precursors have obtained substantial attention in recent years, there is a growing need for fundamental knowledge to uncover interphase formation mechanisms. In this paper, two different types of binding materials, i.e., fly ash-based geopolymer and ordinary portland cement, were mixed with limestone aggregate to examine and compare the microstructures and nanomechanical properties of interphase region. To this end, microstructural characteristics using scanning microscopies, nanomechanical properties by nanoindentation tests, and spatial mapping of chemical contents based on the energy dispersive spectroscopy were integrated to identify and investigate the interphase region formed by the case-specific interactions between the matrix materials and limestone. The...

Study of the Interfacial Transition Zone Characteristics of Geopolymer and Conventional Concretes

“…On the contrary, the SEM microstructure image of the OPC mixture shows large voids/pores around the ITZ, as seen in Figure 3 . This observation agrees well with similar studies [ 21 , 39 ]. Low-density ITZ would compromise OPC mixture properties by weakening the entire mixture.…”

“…One substantial advantage of nanoindentation over micro-indentation is its nano-indent size, and this advantage allows the intrinsic properties of microstructural gradients across the ITZ to be characterized. Studies such as [ 20 , 21 ] were the first that implemented nanoindentation for ITZ characterization. The procedure for sample preparation for the nanoindentation test was developed in [ 20 ], and the interface between fiber–matrix–aggregate was investigated.…”

“…The procedure for sample preparation for the nanoindentation test was developed in [ 20 ], and the interface between fiber–matrix–aggregate was investigated. The nanoindentation was coupled with SEM-EDX and laser scanning to explore the weakest zone in concrete [ 21 ].…”

“…With developments in technology, advanced techniques such as nanoindentation and SEM can be coupled to figure out the ITZs in geopolymer and compare this to the ITZs formed in PC concrete. Nanoindentation can be applied to quantitatively assess the nanomechanical properties of the different phases [ 21 , 33 , 35 ], while the microstructure of ITZs’ phases can be characterized by SEM [ 5 , 21 , 33 ]. In geopolymers, the main reaction product is called sodium aluminosilicate hydrate (N–A–S–H) gel, and the indentation modulus is around the indentation modulus of the main hydration of PC paste product (low-density C–S–H) [ 36 , 37 , 38 ].…”

Effect of Aggregate Types on the Mechanical Properties of Traditional Concrete and Geopolymer Concrete

“…The higher compressive strength of GP made with limestone is probably due to the good bond between the aggregate and geopolymer paste. According to [22], geopolymer paste was observed to be well-bonded to the limestone aggregates in the interphase region in the specimen. In general, the compressive strength of concrete is significantly affected by the strength of binder paste, type of aggregate, and bond strength of ITZ.…”