TROPOLÓGICAS:

The following sub-sections discuss how SCMs, mineral and chemical admixtures affect the hardened properties of the slip form self-consolidating concrete.

4.1.1 Effect of Supplementary Cementitious Materials (SCMs). The effect of high replacement rates of cement by fly ash and silica fume on mechanical properties has been studied by several researchers [68], [98], [99]. Results illustrate that the application of high amounts of FA combined with 10% SF replacement improve the mechanical properties, freeze-thaw and chloride penetration resistance [98]. Higher amounts of fly ash also resulted in a reduction of shrinkage [68]. The total shrinkage of the specimen can be reduced by using fly ash and slag whereas drying shrinkage increased when using silica fume in binary blended mixtures [100]. Celik et al. [101]

investigated the mechanical properties and durability of SCC containing higher proportions of fly ash (up to 50%) and limestone powder (up to 25%). The study stated that the incorporation of fly ash or fly ash with limestone powder resulted in an increase in resistance to chloride penetration compared to mixtures with pure cement and other control mixtures i.e., mixtures blended with 15% and 25% limestone powder. Their results also indicated that the presence of the limestone powder reduces void and pore formation and the hydration of fly ash, resulting in a pore size reduction explaining the increased chloride penetration resistance. Binary mixtures blended with 30% and 50%

fly ash showed lower water absorption compared to control mixtures and ternary

mixtures blended with limestone powder and fly ash. However, for ternary mixtures, increasing the limestone and fly ash content resulted in higher water absorption in mixtures [101].

4.1.2 Effect of Clay Minerals. Metakaolin (MK) replacement can enhance the compressive strength [70], [102], freeze-thaw resistance value [70], [102] and reduced chloride penetration [70] and drying shrinkage [70]. Bumanis et al. [73] indicated that concrete with 15 % MK replacement resisted more than 500 freeze-thaw cycles, chloride penetration was decreased more than 3.7 times compared to the reference mixture and compressive strength of 70 MPa (28 days) was achieved. Garg and Wang [71] investigated the performance of different clay minerals on fly ash-modified mortars. Their results indicated that replacement of up to 15% MK led to an increase in compressive strength. However, other clay minerals such as Kaolin enhanced the compressive strength only by 5-10% and attapulgite clay showed minimal effect on strength [71]. It has also been found that all clay minerals led to higher rate of heat generation i.e. acceleration of hydration process and reduction in setting time due to its finer size and filler effect [71]. The field investigation conducted by Iowa state University and Northwestern University also stated that SFSCC with attapulgite clay resulted in similar compressive strength compared to conventional concrete mixtures for pavements [10]. Also, SFSCC with attapulgite clay displayed less deterioration in freeze-thaw durability and scaling compared to other concrete mixtures. The results presented that all SFSCC mixtures were more freeze-thaw durable compared to conventional concrete pavement mixtures. Furthermore, an addition of up to 1% of nano-limestone increased the compressive strength but this decreased with further increasing dosage [70]. A compressive strength of more than 40 MPa was achieved in [70].

Wang et al. [70] reported that the incorporation of nano-limestone (1%) in SFSCC mixtures led to an increase in compressive strength and freezing-thawing resistance while drying shrinkage and chloride penetration decreased. Clay minerals used in fly ash-modified concrete mixtures for slip form paving [103] indicated that low dosages (up to 2%) of clay showed similar shrinkage and cracking behavior as conventional slip form concrete. The addition of attapulgite clay and kaolin led to an increase in drying shrinkage, whereas metakaolin reduced it. Also, the incorporation of attapulgite clay and metakaolin displayed cracking at earlier age in SCC with fly ash.

However, for other hardened properties, such as compressive strength and splitting tensile strength all SFSCC exhibited comparable performance to conventional concrete [104]. The small difference was found between the compressive strength values of loosely filled (non-vibrated) and vibrated cylinders cast from the same mixture as evaluated by Pekmezci et al. [9] and Armaghani et al. [69].

4.1.3 Effect of Chemical Admixtures. The addition of shrinkage reducing admixture (SRA) or super-adsorbent polymers (SAP) can result in a decrease in compressive strength [75], [105]. Han et al. [75] also concluded that SAP is beneficial for the reduction of autogenous shrinkage at later ages while SRA performed better than SAP for drying shrinkage reduction. Wang et al. [105] stated that to control the loss in compressive strength, it is necessary to control the dosage of SAP and its entrained water content. The use of SRA can result in a significant decrease of drying shrinkage of SCC by reducing surface tension [106], [107], [108]. As both SRA and VMA increase the viscosity of the pore fluid [109], they may help reducing evaporation and change the rate of drying shrinkage. However, no impact was found in drying shrinkage of high strength SCC containing VMA [110].

The effect of SRA was investigated in the field study of SFSCC for slip form pavement [10]. The results indicated that low dosages (2.5 1/m³) of SRA decreased the shrinkage property effectively whereas a higher dosage (7.5 1/m³) not only decreased the amount of drying shrinkage but also diminished the cracking phenomena in the pavement. Heikal et al. [111] investigated the influence of PCE superplasticizer on compressive strength of cement paste containing silica fume. The authors indicated that compressive strength of ordinary Portland cement (OPC) paste was higher than OPC containing silica fume in absence of superplasticizer, however between 0.75-1.5 wt % PCE the compressive strength of OPC with silica fume was higher than OPC.