Effect of clinker grinding aids on flow of cement-based materials Joseph J. Assaad a, ⁎, Camille A. Issa b,1 a Holderchem Building Chemicals, P.O. Box 40206, Lebanon b Lebanese American University, P.O. Box 36, Lebanon abstract article info Article history: Received 9 December 2013 Accepted 17 April 2014 Available online xxxx Keywords: Grinding (A) Rhelogy (A) Fineness (A) Hydration (A) Clinker (D) Grinding aids (GAs) are increasingly used during cement production to reduce energy consumption and/or optimize clinker factor. This paper seeks to assess the effect of such additions on variations in flow of cement pastes, including static yield stress (τ 0 ) and viscosity (η). Grinding tests were performed at fixed specific energy consumption (Ec) or Blaine cement fineness. For fixed Ec, tests have showed that the increase in cement fineness resulting from the addition of higher GA concentration leads to reduced flow and increased τ 0 and η values. Conversely, cement ground for fixed Blaine fineness exhibited an improvement in flowability together with reduction in τ 0 and η values. This was related to a dispersion effect of cement agglomerates in the presence of GA molecules. Special emphasis is placed throughout this paper regarding the effect of GAs on ASTM C465 requirements. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Grinding aids (GAs) are incorporated during comminution of clinker to reduce electrostatic forces and minimize agglomeration of cement grains [1–3]. Their chemical basis mostly includes ethanol- amines such as monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA) as well as glycols such as propylene glycol (PG), monoethylene glycol (MEG), and diethylene glycol (DEG). Because of their highly organic polar nature, GAs are preferentially adsorbed on surfaces formed by the fracture of electrovalent bonds (Ca\O and Si\O), thus reducing surface energy forces. Such additions are commonly used to increase cement fineness and compressive strength for given specific energy consumption (Ec) [1,2]. This could be particularly the case when producing cement possessing increased Blaine fineness necessary for high early strength requirements (i.e., ASTM C150 Type III cement [4]). Nevertheless, with today's con- straints regarding the reduction of usable energy, GAs are more and more used to reduce Ec for given fineness, thereby leading to savings in electrical energy and improved mill productivity [1,3,5]. Typical GA dosage rates used during grinding of clinker vary from 0.01% to 0.15% of the manufactured cement mass. After the grinding process, GAs may not preserve their original mol- ecule structures; however, they do remain adsorbed onto the cement particles to entail variations of cement properties whether in the fresh or hardened states. The setting and hardening properties of cement containing GAs are well documented in literature. For instance, Ramachandran reported that TEA retards hydration of C 3 S and β-C 2 S together with some changes in morphology and microstructure of the hydration products [6]. The hydration of C 3 A was accelerated in the presence of TEA due to the accelerated formation of hexagonal alumi- nate hydrate and its transformation to a cubic form [6]. Heren and Olmez found that the addition of increased ethanolamine concentra- tions alters cement hydration and leads to retardation in setting times in the order of TEA N DEA N MEA [7]. Triisopropanolamine (TIPA), which is an amino-alcohol and belongs to the group of alkanolamines, was found to change hydration reactions and particularly increase cement strengths. Perez et al. reported that TIPA remains in the interstitial paste solution (not adsorbed to the cement surface, as the TEA) and forms iron complexes to accelerate hydration of C 3 S and C 4 AF [8]. Besides the enhancement of alite and felite hydration, Ichikawa et al. presented evidence that TIPA also promotes the hydration of limestone and densifies the interfacial transition zone (ITZ) between hydrated cement paste and sand or aggregate particles [9]. Sandberg and Doncaster reported that the strength increase resulting from the presence of TIPA is not solely dependent on an ITZ mechanism [10]. The strength gain observed in hydrated cement pastes suggested that TIPA is capable to enhance mechanical properties without any paste- aggregate ITZ, regardless of the cement type and age of testing [10]. 2. Context and objectives of this project Limited data exits in literature pertaining to the effect of GAs on flow of cement-based materials. In fact, current literature has extensively Cement and Concrete Research 63 (2014) 1–11 ⁎ Corresponding author. Tel.: +961 3 437786; fax: +961 5 921118. E-mail address: joseph.assaad@lau.edu.lb (J.J. Assaad). 1 Tel.: +961 3 022682; fax: +961 9 547254. http://dx.doi.org/10.1016/j.cemconres.2014.04.006 0008-8846/© 2014 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Cement and Concrete Research journal homepage: http://ees.elsevier.com/CEMCON/default.asp