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The optimized use of nanomaterials in concrete for developing resilient and eco-friendly infrastructure is vital for our built environment. Therefore, the current study aims to optimize the dosages and particle sizes of colloidal nano-silica in developing high-performance, sustainable cement mortar. For this purpose, compressive strength, water absorption, porosity, and microstructure tests were performed on mortars containing different dosages and particle sizes (NS80, NS250, NS250Al, NS500) of colloidal nano-silica. For comparison, tests were also performed on control mortars and mortars containing metakaolin and silica fume. The microstructure of cement pastes was examined through SEM-based BSE imaging with elemental mapping through EDS and FTIR analyses. Additionally, global warming potential (GWP) as well as embodied energy (EE) were also analyzed for all mortar mixtures. The results demonstrated that smaller nano-sized particles (NS500) at a lower dosage (3%) showed improved compressive strength and densified microstructure compared to all other mixes. However, larger nano-sized particles (NS80) at medium (5%) and high dosages (10%) had the highest impact on compressive strengths due to the formation of low and medium Ca-based C-S-H and C-A-S-H phases. Furthermore, the results of greater compressive strength of NS80 mortars under medium and high dosages were supported by their lowest water absorption and apparent porosity. When compared with the control and all other mixes, the mortar mixes containing medium and high doses of NS80 had lower embodied energy/MPa and CO2-eq intensity/MPa, indicating their significant contribution to producing green concrete with a lower environmental impact.

Effect of steam curing regimes on high-performance green concrete (HPGC) has been studied. The concrete was steam cured under three different steam curing regimes with temperatures of 50 °C, 65 °C, and 80 °C and durations of 6, 11, and 16 h. In addition, the replacement level of palm oil fuel ash (U-POFA), which was an experimental variable, was 0%, 20%, 40%, and 60% by weight of cement. The compressive strength (CS), initial surface absorption, porosity, water absorption, gas permeability, and water permeability were tested at 3, 7, 28, 90, 180, and 360 days. The results of the study showed that the utilization of U-POFA in HGPC led to a reduction at the early age CS of the HPGC up to 3 days. However, concrete mixes made with U-POFA showed higher CS at 28–360 days. U-POFA incorporation improved the transport properties of the concrete, with U-POFA60 mix exhibiting the most significant improvement. While application of higher curing temperature tends to impair the properties of the HPGC, longer steam curing period appears to provide a positive effect than shorter duration. The use of U-POFA lessens the negative impact of steam curing on the long-term transport properties of the HPGC. The use of U-POFA at 60% of the weight of the cement achieved CS of 115.8 and 116.9 MPa at 360 days under normal and steam curing, respectively. At the same time, the water absorption was 3.13% and 2.29% under normal and steam curing, respectively.

This work aims to study the influence of milling process on particle size reduction and reactivity improvement of palm oil fuel ash (POFA) as raw materials for the production alkali activated products. Specifically, the quantity of material milled (designated as Q) and the period of milling (designated as M) were the two factors investigated. The amount of milled POFA was examined at six different levels from 1 kg to 5.5 kg (designated as Q1 to Q6). While three milling periods were fixed at 8, 16 and 24 h (designated as M1, M2 and M3, respectively) to obtain the optimum milling process. A total of eighteen mixes of alkali activated mortars were prepared using mixtures of dry source material of milled POFA (GPOFA) and alkaline activator solution from NaOH and Na2SiO3. These eighteen mixes were divided into three different groups based on the periods of milling as M1, M2, and M3. The performance of the samples was evaluated by compressive strength, flexural strength, ultrasonic pulse velocity (UPV), porosity, and water absorption. Chemical and microstructural analyses via X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), and scanning electron microscopy (SEM/EDX) were undertaken to further quantify the performance of the alkali activated mortar. The results revealed that the specific surface area of POFA was increased from 193 m2 /kg to 1710 m2 /kg at the optimum milled quantity of 3 kg and milling period of 24 hrs. The alkali activated mortar based on the ultrafine particle of GPOFA produced a maximum compressive strength (57.5 MPa), flexural strength (10.9 MPa), porosity (13.1%), water absorption (6.2%), ultrasonic pulse velocity (3846.1 m/s) and density (2110.4 kg/m3) at 28 days of curing. The superior results were linked to the formation of greater volume of main binding phases consisting of a calcium silicate hydrate (C-S-H) gel, which was formed within the GPOFA-based alkali activated mortar. Therefore, this optimum GPOFA can be used as alternative to other source materials in the manufacture of alkali activated products and become a sustainable option for solving the waste disposal in the palm oil industry.