Influence of Supplementary Cementitious Materials and Coarse Aggregates on Properties of the No-Fines Concrete

Abstract

The rapid increase in infrastructural development escalates the problem of storm water runoff and flash flooding in rainy seasons in urban areas due to insufficient drainage. To overcome this problem, the permeability of conventional pavements is improved by replacing normal concrete with Pervious Concrete or No-Fines Concrete (NFC). Since NFC consist of extensive large volume of voids which contributes towards its highly porous nature, which can remedy the problem of the rainwater runoff, recharges the groundwater table near road pavements, city streets, and parking lots, and reduces noise from the vehicle tire movement. The exclusion of sand from NFC leads to a reduction in workability and strength, limiting its practical applications. Thereby, it is currently not feasible to use NFC mixtures in highway pavements due to their lower strength than conventional pavement quality concrete. This research aimed to investigate the influence of supplementary cementitious materials such as fly ash, metakaolin, silica fume, and rice husk ash and different gradations of coarse aggregates on the properties of NFC. In NFC mixes, cement was replaced by supplementary cementitious materials up to 20% replacement levels. The effect of different gradations of coarse aggregates on the properties of NFC was also inspected. The following properties were evaluated: compressive strength, split tensile strength, flexural strength, abrasion resistance, water permeability, porosity, density, water absorption, and drying shrinkage up to 365-day. The experimental results indicate that with the inclusion of Fly Ash (FA), the compressive strength decreased at an early curing age up to 28-day compared to the control NFC mix. The compressive strength increased concerning the control NFC mix at 90 and 365-day of curing. With the incorporation of metakaolin in the NFC mix, the compressive strength increased with the increasing percentage replacement of Metakaolin (MK) at all curing ages compared to the control NFC mix. The optimum replacement level for SF was found to be 10% in terms of compressive strength at all curing ages compared to the control mix. The Rice Husk Ash (RHA) replacement reduced the compressive strength at 7 and 28-day. However, at later ages, the compressive strength was maximum at optimum 5% replacement. The overall compressive strength values were higher than the control mix at all percentage replacement levels. The maximum compressive strength of 10.77 MPa was achieved at 365-day in NFC prepared with an aggregate size of 4.75 mm. On replacing cement with FA, split tensile strength results seemed to follow the compressive strength trend with decreases at 7 and 28-day compared to control NFC but improved at 90-day. Hence, it can be concluded that no significant contribution by FA replacement in compressive and tensile strength is observed at early ages as it requires a longer curing period to reach strength comparable to cement. For MK replacement of cement, the split tensile strength increased at different curing ages. For SF in NFC mixes, an increase in split tensile strength at 7, 28, 90, and 365-day with an optimum replacement level of 10% compared with that of the control mix. When replacing cement with RHA, the split tensile strength decreased continuously as the percentage replacement level increased from 0% to 20% compared to the control mix. The NFC mix prepared with smaller-sized aggregates shows better split tensile strength than the NFC mixes made with larger ones. Similar results were found in the flexural strength of NFC containing FA. The trends of flexural strength were similar to compressive and split tensile strength results of NFC mixes with different aggregates sizes such that the smaller size aggregates performed better than larger sized aggregates in NFC mixes. The abrasion resistance increases as the amount of FA and MK replacement increases. The optimum level concerning abrasion was at 10% replacement with SF. In NFC mixes containing RHA, percentage mass loss consistently increased with increasing replacement increased with RHA, causing a drop in abrasion resistance. On the other hand, it was observed that the weight loss was more in NFC-9.5 mm size of aggregate concrete than the NFC-4.75 mm size aggregate concrete. Permeation properties i.e., water permeability and porosity of NFC mixes containing MK slightly reduced but are well within acceptable limits as per ACI guidelines. On the other hand, increased FA levels in NFC mixes decreased water permeability and porosity due to pore size refinement and continuous voids. The permeability properties of permeability and porosity decrease marginally with increasing SF and RHA replacement at optimum levels without considerably affecting the drainage properties for use in road pavements. The permeation properties of NFC mixes improved slightly by using larger size aggregates. The water permeability of NFC mix prepared with 4.75 mm aggregates was 50% lower at 28-day as compared to NFC mix prepared with 9.5 mm sized aggregate. The density of all NFC mixes prepared with FA, MK, SF, and RHA was reported in the acceptable range of 1600 to 2200 kg/m3. The density of the NFC mixes decreases as the size of aggregates used increases. The maximum density was obtained with NFC-4.75 at all the curing ages. The decrease in water absorption values was observed with increasing FA, MK, SF, and RHA replacement of cement in NFC but lies well within the acceptable limits for NFC. Similarly, the drying shrinkage values decreased with the increasing replacement of FA, MK, SF, and RHA compared to the control mix at all periods. From the SEM analysis of different NFC mixes prepared with FA, a refinement in pore structure is observed at later ages due to the formation of higher amount of C-S-H gel. Similarly, NFC mixes prepared by replacing cement with MK show higher concentration of C-S-H gel formation leading to a dense microstructure and higher strengths at all ages. It is also well corroborated by the XRD spectrum; wherein additional C-S-H gel peaks are observed due to this consequent decrease in the peak of quartz. Similar observations are made with replacement of up to 10% of cement with SF. XRD spectrum indicates that major phases formed in NFC mixes prepared by replacement of cement with SF and RHA remain the same. But an additional peak of C-S-H gel is observed in the NFC-SF10 mix accompanied by peak of quartz. In RHA replacement, the primary phase was quartz, which does not participate in the pozzolanic activity. Microstructural analysis of NFC mixes prepared by using different gradation of natural coarse aggregates show the denser microstructure in NFC prepared with smaller sized aggregates at each curing age.