Magazine of Concrete Research http://dx.doi.org/10.1680/macr.11.00082 Paper 1100082 Received 11/05/2011; revised 23/10/2011; accepted 25/11/2011 Thomas Telford Ltd & 2012 Magazine of Concrete Research Green and durable mortar produced with milled waste glass Nassar and Soroushian Green and durable mortar produced with milled waste glass Roz-Ud-Din Nassar Research Associate, Civil and Environmental Engineering Department, Michigan State University, USA Parviz Soroushian Professor, Civil and Environmental Engineering at Michigan State University, USA The concept of using milled waste glass as partial replacement for cement in cement paste and mortar was investigated to reduce the adverse environmental and energy impacts of cement and cement-based products. Based on the experimental investigations it was found that waste glass, when milled to micro-scale particle size, undergoes pozzolanic reaction with cement hydrates. These reactions bring about favourable changes in the structure, including pore system characteristics of the hydrated cement paste and mortar. Use of milled waste glass, as partial replacement of cement, produced significant gains in the resistance to moisture sorption, chemical stability and improvement in microstructure of the cementitious materials. Milled waste glass was also found to suppress alkali– silica reactions. Unlike normal pozzolanic reactions, those involving glass do not reduce the alkalinity of cement paste; this is favourable to the chemical stability of cement-based materials and the protection of reinforcing steel against corrosion in concrete. Introduction The production of cement is a highly polluting process, which contributes about 5 to 8% to global carbon dioxide (CO 2 ) emissions, and accounts for 3% of total (5% of industrial) energy consumption worldwide (Gartner, 2004; Naik, 2008; Van Oss and Padovani, 2003; World Energy Council, 1995; Worrell et al., 2001). Production of each tonne of cement results in the emission of about 0 . 9 t of carbon dioxide to the atmosphere (EPA, 2010; USGS, 2005). Carbon dioxide is a by-product of the chemical reactions involved in the production of cement (chiefly decarbo- nation of limestone); the energy consumed in the course of cement production is another source of carbon dioxide emissions. The estimated total carbon emissions from cement production plants were 1 . 22 billion tonnes in 2002, which rose to about 1 . 8 billion tonnes in 2004 (compared to total worldwide carbon dioxide emissions of 25 billion tonnes in 2004) (UN, 2009). In 2007, the total cement production in the United States was close to 90 million tonnes, which contributed about 90 million tonnes of carbon dioxide to the atmosphere (USGS, 2008), whereas global cement consumption was 2 . 75 billion tonnes. This shows the large carbon footprint of the industry (Mehta, 2009). The 1995 carbon dioxide emissions from the cement industry were equivalent to the emission from 300 million automobiles (Mal- hotra, 2000). Cement production also involves emission of moderate quantities of NO x (nitrogen oxides) SO x (sulfur oxides) and particulates (Van Oss and Padovani, 2003). Cement manufacturing is an energy-intensive process which is also a major source of greenhouse gas emissions. It ranks third after aluminium and steel manufacture in terms of energy consumption. Close to 5 . 8 GJ of energy are consumed in the production of a tonne of cement (Naik and Kraus, 1999). The energy used for the production of cement accounts for more than 90% of the total energy required for the production of concrete (BuildingGreen.com, 2004). In spite of major efforts in recent decades, significant gains in the fuel efficiency of cement production plants has not been realised (Gartner, 2004). This situation warrants decisive measures to be taken to reduce the carbon contribution of the cement and concrete industry. The growing environmental concerns and the increasing scarcity of landfills encourage the recycling of the landfill-bound constitu- ents of the municipal waste stream, including glass which occurs largely as mixed-colour waste glass with a limited market value. The waste glass generated in the US in 2008 was about 11 million tonnes, 77% of which was disposed off in landfills (EPA, 2009). Mixed-colour waste glass, however, offers desired chemi- cal composition and reactivity for use as a supplementary cementitious material (SCM) for enhancing the chemical stability, pore system characteristics, moisture resistance and durability of cementitious paste and mortar. To realise this potential, waste glass needs to be milled to micro-scale particle size for accelerat- ing its beneficial chemical reactions (Dyer and Dhir, 2001a; Dhir et al., 2009). Owing to the presence of amorphous silica in glass and also the alkaline nature of glass (Na 2 O (sodium oxide) . 13% by mass), the idea of using glass in cement-based materials has traditionally 1