**1. Introduction**

Economic development inevitably increases construction activity, which depends heavily on the production of cement. The most direct approach to reduce the CO2 emissions associated with the manufacture of cement is to reduce cement consumption or replace cement with other pozzolanic materials (e.g., industrial by-products) with similar binding properties [1–3]. Non-cement blended materials can help to reduce construction costs and the negative impact of cement production on the natural environment [4,5]. Considerable advances have been made in the conversion of waste materials into usable resources [6,7], thereby reducing the space required for waste storage and helping to conserve natural resources [8,9].

Researchers have demonstrated that the incorporation of pozzolans as a partial replacement for cement can improve the mechanical properties and durability of the resulting concrete [10–12]. Numerous studies have also used pozzolans (fly ash or slag) to entirely replace cement in ordinary concrete or mortar. Many specimens have strength, mechanical properties and durability superior to those of conventional concrete [13,14]. The key factor in achieving a fully hydrated reaction without cement is the inclusion of an alkali activator or the enactment of curing at an elevated temperature. The cementless composites containing alkali activators inevitably increase production costs. However, many industrial by-products can be used as alkali activators to save cost due to its chemical composition with higher alkali contents.

Considerable advances have been made in the low-energy manufacture of non-cement blended materials, particularly in Taiwan, Korea and Japan. Ground-granulated blast-furnace slag can be combined with various supplementary cementitious materials to eliminate the need for alkali activators in the production of materials suitable for civil construction. Many such materials provide high compressive strength (30 MPa to 60 MPa), as well as excellent mechanical properties and durability [15–18]. The inclusion of polypropylene fibers in composites has been shown to enhance the tensile strength and volume stability of non-cement blended materials [19–21]. In recent years, a number of researchers have studied the use of polypropylene fibers or non-cement blended materials; however, there has been little work on the addition of polypropylene fibers to non-cement blended materials. In this study, we combined ground-granulated blast-furnace slag (GGBS) with circulating fluidized bed (CFB) co-fired fly ash and polypropylene fibers to produce non-cement blended materials without alkali activator. Samples were compared with standard Portland cement mortar in terms of mechanical properties, permeability and microstructure. The proposed material is intended to be used as a controlled low-strength material, pervious concrete, reinforced recycled concrete and for other engineering applications [22–24].
