| Beneficial utilization of recycled glass powder (GP) as a supplementary cementitious material has been limited due to the poor knowledge of the interactions between GP and concrete environment. For example, it is seen that the early-age strength of concrete is reduced. This is attributed to the slow rate of GP pozzolanic reaction which begins with dissolution of glass. The hypothesis of this research is that GP dissolution and hence its reactivity can be accelerated by increasing the alkalinity of pore solution. The core objective of this research is to evaluate this hypothesis through a step-by-step experimental method, designed to answer four specific questions: (1) what are the chemical and physical aspects of soda-lime glass dissolution in alkaline solution? (2) Does reactivity of GP with Ca(OH)2 accelerate through use of alkaline solutions? (3) What is the overall performance of concrete, containing GP and mixed using alkaline solutions? (4) What are the micro-scale mechanical properties of the cementitious products of GP in concrete in comparison to conventional cementitious materials?;To answer the first question, this research conducts a fundamental analysis of the interactions between soda-lime glass and concentrated NaOH solutions. Along with measurement of the kinetic parameters of glass dissolution, the characteristics of solid products forming as a consequence of soda-lime glass dissolution is studied using characterization techniques. It is shown that 1M NaOH solution is more corrosive than other concentrations, with activation energy of dissolution measured as ≈85 kJ/mole. Addition of Ca(OH) 2 to 1M NaOH solution decreases the rate of glass dissolution. It is also found that due to the presence of calcium in soda-lime glass, dissolution is accompanied by formation of semi-crystalline calcium silicate hydrate (C-S-H) materials.;To answer the second question, pastes of GP-Ca(OH)2 are prepared by mixing with water or NaOH solutions and the reaction rate, stoichiometry and characteristics of the reaction products between GP and Ca(OH)2 are investigated. It is concluded that NaOH solution can significantly accelerate the rate of the reaction between GP and Ca(OH)2 to form C-S-H products.;To answer the third question, the compressive strength of four mortar systems containing GP are evaluated, focusing on the use of alkaline solutions. These include mortars prepared by the binary phases of GP-Ca(OH)2, GP-portland cement(PC), GP-slag and GP-fly ash. While alkaline solutions are helpful in the first system, the low absolute strength values limit its application. Also, due to a severe detrimental effect of alkaline solutions on hydration of PC, the use of alkaline solution in PC-based systems is not justified. However, due to compatibility of slag and fly ash to alkaline solution, these systems are found to be appropriate host concretes for GP, enriching the binding phases with silica.;Finally, micro-scale mechanical properties of the cementitious phase formed due to pozzolanic reaction of glass is studied using peak force tapping AFM, and compared to hydration products of PC, alkali activated slag and fly ash systems. Due to the very small induced deformation (3-5nm), surface topography becomes super critical. The measured modulus values are lower than the available literature data, usually assessed using conventional indentation techniques. |
