AdvancesinCementResearch,2003,15,No.,Month,1±9 Effect of complex admixtures on cement properties and the development of a test procedure for the evaluation of high-strength cements K. Sobolevà European University of Lefke Recent research has shown that a state-of-the-art process for high-performance HP) cement adds a new dimension to `classical'cement technology. The key idea of the process involves the mechano-chemical activation of cement at the grinding stage. A silica-based complex admixture is used for the activation of the cement imparting high strength and improved durability to mortars and concrete. This paper describes the effect of different complex admixtures on the strength of HP cement. According to the available results, mortars based on HP cement possess a compressive strength of up to 148 MPa. A comparison of alternative evaluation methods helps to recommend the test procedure for HP and high-strength cement. Notation The additional letter after the main notation identifies The following notation were applied to distinguish the of the test procedure as follows samples I reference Portland cement CEM-I 42´5 NPC-# reference Portland cement 'without additional grinding) LWDB-# reference low water demand binder W for EN 196 mortars 'constant w/c) HPC-A-# reference high performance cement type A F for ASTM C109 mortars 'constant flow) HPC-BS-# reference high performance cement type B S for ASTM C387 mortars 'variable S/C) '50% of GBFS) HPC-BL-# reference high performance cement type B '35% of LS) SFC-# high performance cement produced using Introduction SF admixture The latest developments in cement and concrete MSC-# high performance cement produced using science show the following trends1,2 MS admixture MKC-# high performance cement produced using 'a) Increasing strength: major breakthroughs in know- MK admixture ledge have led to the design of cement based materials with greater strength; this has resulted in the development and application of super high- strength concretes with a compressive strength of up à Department of Civil Engineering, European University of Lefke, to 135±250 MPa, high flexural strength and im- TRNC. proved ductility.3±12 'ACR 419) Paper received ?? ?????? ????; last revised ?? ?????? 'b) Application of chemical admixtures: added to the ????; accepted ?? ?????? ???? concrete mixture, relatively small amounts of 1 0951-7197 # 2003 Thomas Telford Ltd Article number = 2419 K. Sobolev chemical admixtures can alter the behaviour of fresh products have been developed. Well-known examples or hardened concrete. Chemical admixtures can include air-entraining, hydrophobic and plasticised ce- improve almost any problematic property of con- ments, and also the family of cements that are manu- crete: they are one of the essential components of factured using grinding aids. It has been suggested that modern concrete that help control strength and the action of these modifiers is based on mechano- durability.13,14 chemical activation.19 'c) Utilization of industrial by-products and waste The theory of mechano-chemical activation has been 'IBPW): the use of IBPW as mineral additives has successfully applied to processing nanopowders, pig- become an important part in cement and concrete ments, fillers, binders, ceramic and ferromagnetic technology. According to wide- ranging in- materials. Using this method, an improvement of ce- vestigations,1,2,13±16 the performance of conventional ment strength can also be achieved.19,20,23,26 Low water concrete can be significantly improved by adding demand binder 'LWDB) is produced by intergrinding IBPW in specific quantities. Well-known mineral cement and a dry modifier at a high energy.25 In spite additives include granulated blast furnace slag, fly of a similar technique already suggested by Royak and ash and silica fume. These mineral additives not only Royak, and Skvara et al.,19,20 only the application of a yield a concrete that has better properties and is more specially selected admixture-modifier at a relatively cost effective, but they also reduce the environmental high dosage 'up to 4%) resulted in the manufacture of impact of construction activities.16 a cement with both reduced water demand and high strength. Following these developments, the concept of high The group of mineral and organic complex admix- performance concrete 'HPC) has been put forward and tures for application in cement technology has been successfully applied worldwide. It is generally accepted proposed.18 Basically, these admixtures contain a reac- that concrete with improved properties 'workability, tive silica-based sorbent as a mineral constituent and a strength, permeability, durability, etc.) above the con- surfactant as its organic constituent plus some minor ventional benchmarks can be specified as HPC. Ac- corrective admixtures 'Fig. 1, further details are pro- cording to Forster,17 HPC is `a concrete made with vided in Reference18). Supersilica, a reactive silica- appropriate materials combined according to a selected based complex admixture was developed using this mix design and properly mixed, transported, placed, principle.16,18 Although all the effects of supersilica consolidated, and cured so that the resulting concrete have not been completely investigated, it is hypothe- will give excellent performance in the structure in sised that, when added during the cement grinding which it will be exposed, and with the loads to which it will be subjected for its design life'. To realize the HPC concept, a range of chemical Reactive admixtures and mineral additives are required, and Surfactant consequently, a modern concrete batching plant must silica use appropriate equipment for precise control, dispatch- ing, dosing and batch processing.7±14 This modernisa- tion of production facilities is an unavoidable cost for Mixing improved performance since variations in dosing or granulating mixing the components of the concrete may affect the performance of the final product. The compatibility of the admixtures is yet another problem for the produc- 13,14 Complex tion and application of HPC. admixture However, an alternative method for controlling con- crete properties and the design of HPC is the use of special cements possessing higher strength and better Gypsum Grinding resistance to the deterioration caused by various physi- ball mill cal, chemical and mechanical factors.18±26 These super- Clinker ior cements are often based on special clinkers or blended cements such as shrinkage compensating or expansive cements, high early strength cements, regu- IBPW lated-set and jet-cements.3 The group of these cements also includes newly developed Ultimax cement, blended Pyrament and SF cements.20±24 The application of chemical admixtures offers an HP cement advanced approach to improving cement performance; modifing the cement grinding process.19 Using this method, a number of chemical admixtures and cement Fig. 1. Flow chart of HP cement technology 2 Advances in Cement Research, 2003, 15, No. 1 Effect of complex admixtures on cement properties: a test procedures process, supersilica modifies the surface of cement Research significance particles and also promotes the formation of highly reactive amorphous structures and pre-hydrates.18 The effect of silica fume on the behaviour of ce- Further, the reactive silica component also acts as a ment-based materials has been extensively reported in micro-filler and participates in a pozzolanic reaction. the literature.1±14 A number of published papers on HP The mechano-chemical activation of cement with cement deals with the application of a silica fume supersilica at the grinding stage results in a high based complex admixture.16,26 At the same time the use performance 'HP) cement. of other types of reactive silica products as a compo- HP cement can be defined as a product manufac- nent of the complex admixture has been proposed.18 tured by the mechano-chemical activation of certain Consequently, the evaluation of the effect of different proportions of clinker, gypsum, complex admixture reactive silica materials on the cement strength is and, optionally, a mineral additive of industrial 'IBPW) important for the manufacture and practical application or natural origin 'Fig. 1), which imparts high strength of HP cement based materials. and extreme durability to the concrete or mortar made from such cement.18,26 Such high strength can be used for the engineering of a cement with high volume Experimental programme mineral additives 'HVMA). As a result, relatively large amounts 'up to 70%) of portland cement clinker can be Materials used replaced with inexpensive locally available mineral Three different reactive silica components were used additives. Natural pozzolanic materials, sand, lime- in the complex admixture: silica fume 'SF), natural stone, granulated blast furnace slag, fly ash, glass cullet microsilica 'MS) and metakaolin 'MK). The reference and ceramic waste, all can be used as mineral additives cements were: Portland cement CEM-I 42´527 'NPC-I, 16 in HVMA cements. type I according to ASTM C15028) and low water There are two types of HP cement: type A basic HP demand binder 'LWDB). The samples of optimised cement; and type B blended HP cement. Basic type A high-performance cement type A 'HPC-A) and type B cement involves intergrinding the clinker, gypsum with 'HPC-BS containing 50% of GBFS and HPC-BL a complex admixture. Blended type B cement covers a containing 35% of limestone, LS) were also tested for wide range of HP cements with mineral additives. The comparison.26 The chemical composition of these content of a mineral additive in blended HP cement materials is presented in Table 1. It is noticed that due varies with the specified level of the properties and to a high volume of GBFS, HPC-BS had a relatively 16 with the type of additive used. Preliminary research high MgO content, but no subsequent expansion of demonstrated that type B blended HP cements with a cement was observed during the hardening. The parti- mineral additive content within the standard limitations cle size distribution of some selected cement samples is 27 '25±50% as specified in EN 197-1, ) can be produced.