Mix Design and Engineering Properties of Fiber-Reinforced Previous Concrete Using Lightweight Aggregates  
[PERSON]  
1 Department of Civil Engineering and Geomatics, Cheng Shiu University, No. 840, Chengching Rd. is not good. In contrast, PC has connected pores and its water permeability is excellent [7; 8; 9]. When pouring and compacting PC, the aggregates adhere tightly to each other, exhibiting interconnected pores. In the fresh plastic state, the general PC is relatively viscous and its slump is usually less than 20 mm. Since PC exhibits low workability, it is meaningless to evaluate the workability of PC. In other words, the slump of PC has nothing to do with its workability and is not suitable as an acceptance criterion [10; 11]. When pouring PC on a construction site, in order to ensure sufficient working time, a retarder or hydration stabilizer is often used [10; 11]. In addition, viscous agents can also be blended to avoid the paste draining down and improve the workability [10; 11]. In general, the composition of PC lacks fine aggregates, which gives it a high porosity. This allows air or water to move in the concrete and gives it a lower unit weight [12]. Typical PC materials are composed of narrow gradation (homogeneous or gap-graded) coarse aggregates, no fine aggregates (or trace amounts), and insufficient amounts of cement paste so that the internal porosity of the material is high and forms a network with interconnected pores [13; 14]. However, in practical applications, the design of PC as a pavement material should take into account both porosity and structural strength [15]. Overall, compared with ordinary concrete, PC has the following characteristics: low bulk density, low thermal conductivity, insignificant capillary phenomena (average pore diameter greater than 1 mm), near-zero slump, no segregation, low shrinkage, low cost, and small side pressure during molding [16]. For the hardened properties of PC, its typical density or unit weight, porosity, permeability, compressive strength, and flexural strength are shown in Table 1[17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40]. The range of compressive strength of the PC shown in Table 1 is quite wide, about 2.6-61.2 MPa. In addition, the freeze-thaw resistance of PC in harsh environments has also attracted researchers' attention. Research by [PERSON] et al [41] showed that the freeze-thaw durability of PC reinforced by polypropylene fibers with various nominal lengths was significantly improved. Some researchers believe that due to the high permeability of PC, its pore structure cannot be saturated with water; therefore, freeze-thaw damage generally does not occur [42; 43]. However, there have been many actual cases showing the opposite result. Due to its specific use function and service conditions, even under unsaturated or partially saturated conditions, PC in cold climates is more susceptible to freeze-thaw damage than ordinary concrete [44; 45]. On the other hand, it is particularly noteworthy that the use of lightweight aggregates not only significantly reduces the unit weight of PC but also enhances its thermal insulation properties [46]. These excellent properties make PC an environmentally friendly material. Despite this, the use of lightweight aggregates has some disadvantages, such as the reduced mechanical properties of PC [46; 47; 48]. From the data listed in Table 2, compared with general PC, the mechanical properties of PC made of lightweight aggregates are significantly reduced. Taking the important mechanical properties of lightweight pervious concrete (LPC) as an example, the compressive strength test results are about 1.80-5.99 MPa. Improving the mechanical properties of PC to promote its application range has been widely researched. Overall, findings consistently confirm that the use of suitable materials and proper mix proportions are critical factors [49; 50; 51; 52].