Specialty Chemical for Portland Cement Concrete towards Sustainable Construction Material

用於製備可持續發展矽酸鹽水泥混凝土的特殊化學試劑研究

Student thesis: Doctoral Thesis

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Detail(s)

Awarding Institution
Supervisors/Advisors
Award date14 Aug 2018

Abstract

Portland cement concrete (PCC) is the composite with filler of aggregate glued by hydrated Portland cement (PC) acting as a matrix. PCC as the most used construction material is irreplaceable in foreseen future by other material. Sustainable feasibility of PCC as construction material lies on PCC production competitiveness in terms of natural resources, ecology and economy. Although PCC is considered as eco material per unit quantity, the large concrete consumption contributes a significant portion of all man-made carbon dioxide equivalent (CO2eq) and consequently appears as the major hurdle for the construction material sustainability. Immensely, the main issue lies on the production of PC. Its production releases approximately equal amount CO2eq to the quantity of PC produced. In order to minimize the environmental degrading impact from concrete production the term “sustainable” is promoted for concrete production, which adapts the similar aim of sustainable development. Even though there are various strategies towards the sustainable use of concrete, the most acknowledged effective approach is to minimize the PC consumption per unit time of structural service life. Employing the specialty chemical for construction has been recognized as the most viable approach to minimize PC consumption. The specialty chemicals can be applied during concrete production stage as well as for structural refurbishment. The application during production stage allows the manufacture of strong and durable concrete facilitating structural design optimization. The use for structural refurbishment enables the prolonged service life of existing concrete structure. In this research, the nanoscale characterization employing combined simulation and experimental technique has been performed on the interaction between the commonly used specialty construction chemical and concrete during the stage of its production, curing and service life.

The main concrete characteristic expected from the such mentioned three stages is high rheology, adjustable setting time and long service life, respectively. The chemical examined in this study includes polycarboxylate ether (PCE), triethanolamine (TEA) and epoxy. These three chemicals respectively are employed during concrete production (as dispersant for cement suspension in water), curing (as setting time regulator of hydrated cement) and service life (as bonding agent in refurbishment system). The main factor influencing the dispersing performance of PCE is its molecular conformation that is remain not fully resolved, mainly due to the limited experimental technique. PCE conformation is examined using dissipative particle dynamic (DPD) as coarse grained simulation. The result shows the ball-shaped morphology of PCE in water and the consistency upon its radius of gyration (RG) obtained from the simulation, theory and experiment. Additionally, the simple linear relationship is found between RG and number of monomer in PCE. TEA is a chemical that can have accelerating-retarding effect on the initial setting time of hydrated PC. In this study, it is found that the accelerating-retarding effect of TEA on the initial setting time is caused by the different intensity of formed ettringite, which is governed by the triethanolamine dosage. Epoxy is the bonding agent used in commonly applied concrete strengthening system based on fiber reinforced polymer (FRP) system. Herein, molecular dynamics simulations together with Bell's model are employed to evaluate the effect of sodium chloride solution on the adhesion at interface between epoxy and silica (as one of the major component of concrete). It is shown that sodium chloride solution weakens the adhesion significantly. This finding indicates that the bond deterioration at epoxy-concrete interface is critical in the presence of salt solution, which must be considered in the engineering design strategy for offshore and marine structures. Additionally, it is envisioned that the advance technological progress of specialty construction chemical can eventually help on nano-engineering for “smart” hydrated PC towards the existence multifunction construction material. As an initial motivation towards the outcome of this vision, it is herein reported that applying the polarization process throughout curing of hydrated PC under the influence of an electric field can improve the piezoelectricity of PC hydrates. Significantly, the finding obtained in this study contributes the novel insight understanding upon the chemical-concrete interaction at different stage from concrete production to service life, which can be useful information for technological progress of construction chemical.