Rate of carbonation in cement modified base course material Alireza Rezagholilou a,⇑ , Vagelis G. Papadakis b , Hamid Nikraz c a Department of Petroleum Engineering, Curtin University, Australia b Department of Environmental & Natural Resources Management, School of Engineering, University of Patras, Greece c Department of Civil Engineering, Curtin University, Australia highlights  An analytical model displays a high potential for the estimations of carbonation rate in soil cement.  Carbonation progress is measurable for soil cement materials either analytically or experimentally.  Nanosilica assists in mitigation of deleterious reactions. article info Article history: Received 1 October 2016 Received in revised form 10 May 2017 Accepted 22 May 2017 Available online 14 June 2017 Keywords: Carbonation rate Soil cement Analytical model Pavement and nanosilica abstract In the absence of a carbonation model for soil cement, this research aims to assess the compatibility and applicability of an analytical model initially developed for concrete. Carbonation can be observed in any pavement layer which includes cement or lime. For instance, carbonation damages the cement-modified crushed rocks as a typical material for base course layer due to poor curing of material or cracking of asphalt. Experimental laboratory tests are utilised here in accelerated carbonation conditions to evaluate the analytical model. Cylindrical specimens are subjected to one-dimensional carbonation condition. Weight and ratio of constituents of mixes, as well as environmental factors, such as CO 2 concentration and relative humidity are recorded for analytical estimation of failure progresses. Nanosilica is also intro- duced in mixes to explore its effects during carbonation reactions. Results show linear correlations between experimental records and analytical model calculations. Thus, it can be concluded that carbon- ation rate can be predicted in soil cement also. In addition, the inclusion of nanosilica has a positive influ- ences by slowing of the carbonation progress. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction Carbonation of hydrated cement involves the reaction of carbon dioxide CO 2 with the hydration products. Calcium hydroxide Ca (OH) 2 and calcium silicate hydrate (C-S-H) are attacked by CO 2 in the hydrous voids which exist in cementitious mixtures. Hence, strength developments are stopped or reversed through the pro- duction of calcium carbonate CaCO 3 . These deleterious reactions act to destroy the cementitious bonds of aggregates or soil particles which lead to rutting, spalling and cracking of bituminous layers in pavements [23]. These reactions also reduce the strength, density and elasticity of the material alongside increasing porosity and permeability of stabilised material. In this process, cement treated soils can lose their strength up to 70% which is a significant decrease with respect to load bearing layers in pavements [21]. These reactions can also develop internal expansive forces beyond tensile strength, which weaken or disintegrate soil cements [20]. As such, carbonation is labelled as an unfavourable chemical reac- tion in stabilised soils. Typically in Western Australia, this type of failure has been reported in trial sections of the Kwinana Freeway, Reid highway and taxiway D at the Broome Airport [7,8,30]. Along this line, the carbonation reaction can be initiated even when cement paste is exposed to air during mixing, so it should be limited as far as possible. To date, the latest suggested methods of its control in soil cement are the use of high cement content, early compaction and immediate surface sealing or protection by means of different prime coats including bituminous solutions [22]. Indeed, depth of carbonation in concrete is around 0.5–2 mm after several years [11,15], which is much lower than soil cement. In soil cement, limited observed records indicate that the rates are about 3–50 mm/year in South Africa [17]. This range is high for a base layer with nearly 200 mm thickness that should last for http://dx.doi.org/10.1016/j.conbuildmat.2017.05.226 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: Ali.rezagholilou@curtin.edu.au (A. Rezagholilou). Construction and Building Materials 150 (2017) 646–652 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat