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Fly ash (FA) and granulated blast furnace slag (GBFS) were used as a precursor for geopolymerization to develop a low-carbon pavement base construction material. Based on the orthogonal test method, three levels were set separately for the L9 (34) test considering the proportion of FA (raw fly ash to grained fly ash), ratio of sodium hydroxide to liquid alkaline activator (LAA), and proportion of GBFS mixed with FA and solid–liquid ratio [(FA + GBFS): LAA] as factors influencing the geopolymer. The influence of these factors on the unconfined compressive strength (UCS) of soil stabilized by geopolymer was studied. The optimal combinations of levels and factors were determined. The UCS with these ratios combined was 5.1 MPa. According to the above compositions, the mechanical (UCS, splitting tensile strength, and flexural tensile strength) and durability (drying shrinkage, water stability, freezing and thawing resistance, and wet–dry cycle) properties of soil samples stabilized using the aforementioned geopolymer were investigated. Moreover, scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis were performed to determine the effect of the change in hydration silicate gel in the UCS development. According to the SEM and XRD test results, hydrated silicate gels exist in the sample, filling the pores of the soil, making the soil more compact, bonding the soil particles, and enhancing the engineering performance of the soil. This study enables waste material utilization as a replacement and partially reactive material in pavement applications. [ABSTRACT FROM AUTHOR]

Because of demand uncertainties, a build-operate-transfer (BOT) project may lead a concessionaire either to realize an excessive profit or suffer a loss. The object of this paper is to establish an adjustment mechanism to automatically balance the risks and rewards between public and private sectors under the fixed preset concession period. Using a revised net present value (NPV) financial evaluation model and the Monte Carlo simulation technique, the authors construct a model that can determine the optimum solution of the minimum revenue guarantee (MRG) level and the collect rate of royalty for BOT projects. The MRG and royalty collection combination (G&R) is shown, via a reduction in the decision variables, to be a more effective scheme than those in previous studies. The results of a sensitivity analysis based on a wastewater treatment BOT project prove that Scheme M of MRG based on 90% volume combined with a 20% royalty rate is the leading option because it guarantees that the concessionaire will always earn a reasonable anticipated return under the fixed term. The main contribution of this paper is to provide a simple tool for balancing the risks and benefits for the government and investors. [ABSTRACT FROM AUTHOR]