# Influence of Milling Techniques on the Performance of Wheat Straw Ash in Cement Composites
## 1 Introduction  
Cement is an important component of concrete and it is used widely in the construction industry and expected to be double by 2050 [1]. Worldwide production of cement is an environmental concern due to CO\({}_{2}\) emission during the cement production. It has been estimated that about 8 kg of carbon dioxide is emitted in the atmosphere while producing 10 kg of cement [1; 2; 3]. This way, the production of cement account for 6-7% of worldwide CO\({}_{2}\) emissions [3]. Apart from this, cement producing plants utilize a huge amount of energy which contributes to 3% of the universal consumption [4]. The CO\({}_{2}\) emissions from cement industry are produced by combustion (30-35%), decomposition of limestone (50-60%), and the transportation of the materials (about 10%) [5]. These emissions can be minimized by incorporating waste or raw materials as partial or full substitute of cement. These materials are most commonly known as supplementary cementitious materials (SCMs) [1]. For this purpose, utilization of SCMs such as fly ash, slag, silica fume, rice husk ash (RHA), wheat straw ash (WSA), etc. in the construction industry is gaining much attention. These materials contain an abundant amount of silicawhich causes excellent pozzolanic activity [6]. The utilization of these materials as substitute of cement can be a feasible solution for the decrease of carbon dioxide emissions [7]. The ashes obtained by burning agricultural residues has been widely used to replace cement. Most commonly used agricultural residue ashes (ARAs) are RHA, rice straw ash (RSA), sugarcane bagasse ash (BA), palm oil fuel ash (POFA), and corncob ash (CCA). [PERSON] [8] and [PERSON] [9] reported that high specific surface area, porous microstructure, and high amount of amorphous silica make RHA make it an effective supplementary cementitious material. It has been reported in various studies that concrete containing RHA depicted improved mechanical performance, minor permeability, and amplified resistance to acid attack, corrosion, and carbonation [10; 11]. In another study, it has been reported that mortar specimens made with 10% substitution of cement with RSA have demonstrated enhanced strength and impermeability compared to control mix [12]. [PERSON] [13] investigated the usage of BA as a possible cement replacement material. He made concrete specimens by replacing cement with 20% of BA and investigated various properties. The results of his study reveal that concrete specimens containing BA displayed reduced chloride penetration and substantial early strength development. [PERSON] et al. [14] stated that improved compressive strength and sulfate resistance was observed for concrete test specimens made with well-ground POFA. The results of the study conducted by [PERSON] and [PERSON] [15] recommend replacement of cement with 8% CCA for structural concrete. Among all agricultural residue ashes, WSA has not been thoroughly studied. Wheat is the major produced cereal crop in the world. In 2017-2018, European Union produced approximately 151.6 million metric tons of wheat and Pakistan produced 26.6 million metric tons of wheat production [16]. During production of every 10 kg of wheat, 13-14 kg of wheat straw is generated [17]. The unused wheat straw is burnt in open atmosphere which is a severe environmental concern. However, WSA is a rich source of silica making it an efficient pozzolanic material. [PERSON] et al. reported that burning wheat straw produced 8.6% of ash (73% silica content) [18]. The efficacy of WSA as a pozzolanic and filler material in cement mixtures is reported in previous research studies [18; 19; 20]. They have concluded that addition of WSA improved the mechanical properties of cementitious composites [18; 19]. Apart from this, WSA has been reported to possess filling property. For instance, in a study, it has been reported that the hardened properties of cement mortars are enhanced due the filling ability of WSA [20].