Since the 1970s, roller compacted concrete had appeared in experimental research in the field of dam construction, which adopted a method that combines the structural characteristics of normal concrete dams with the construction technology of earth-rock dams (Jia et al. 2006). Roller compacted concrete has the advantages of low hydration heat, zero slump, and low cost, making it suitable for constructing large dam structures (Luo et al. 2022). Roller compacted concrete dams combine the structural advantages of traditional concrete dams with the construction technology of earth-rockfill dams, resulting in lower construction costs, higher equipment utilization efficiency, and easier and faster construction compared to traditional concrete dams (Selvam et al. 2022). During the construction of roller compacted concrete dams, the combined action of strong mechanical vibration and rolling compaction was used to compact ultra dry and hard concrete. Due to the layered compaction during construction, there are often many horizontal construction joints in the roller compacted concrete dam, forming numerous horizontal layers (Shen et al. 2001). In experimental research and construction practice (Pacelli et al. 1993; Shen et al. 2023; Liu et al. 2018), it was found that the quality of interlayer bonding had a significant impact on the performance of the roller compacted concrete dam.
Different material ratios, different material parameters, and unsuitable rolling construction techniques can cause local defects in the layer, which affects the stability of layer stress and the performance of the dam body. The adhesiveness of roller compacted concrete mixtures was very poor, and it was easy to cause aggregate separation during transportation and paving. After rolling, it may also result in non compaction, which affects the overall impermeability of the dam (Huang et al. 2017). To reduce or avoid the phenomenon of coarse aggregate separation, in some projects, the maximum particle size and proportion of coarse aggregate are limited, and second-graded or third-graded roller compacted concrete was selected (Jia et al. 2006). Increasing the maximum particle size of coarse aggregate can lessen the porosity of coarse aggregate and require less cementitious material overall. Therefore, how to find the balance point between the two requires extremely detailed experimental determination. Increasing the maximum particle size of coarse aggregate can reduce the porosity of coarse aggregate and reduce the amount of cementitious material used. The maximum particle size of crushed stone is usually limited to below 80mm (Huang et al. 2017). Appropriate aggregate gradation and the ratio of coarse and fine aggregates are key factors in obtaining high-performance roller compacted concrete. The correct selection of aggregates will minimize voids, reduce segregation, and affect water demand. Therefore, determining the maximum size of aggregates and the ratio of coarse and fine aggregates is crucial. Hashemi et al. (2018) investigated the impact of coarse to fine (C/F) aggregate ratio on the performance of two types of roller compacted concretes with cement contents of 9% and 12%, and mechanical performance tests were conducted to determine the hardening performance of roller compacted concrete. The experimental results indicated that increasing the C/F ratio from 0.6 to 1.8 tripled the Vebe time, while increasing the C/F ratio from 0.6 to 1.2 obviously reduced the porosity, and with the increase of the C/F ratio or cement content, the compressive, splitting tensile and bending tensile strengths of the specimens remarkably increased; Li et al. (2015) analyzed the stress and seepage fields of a roller compacted concrete dam with three-graded roller compacted concrete and two-graded roller compacted concrete, and found that the impermeable layer constructed with three-graded roller compacted concrete has comparatively poor permeability resistance, while two-graded roller compacted concrete can improve its permeability resistance but may form seepage channels; Wu et al. (2013) tested the combined compressive properties of concrete specimens with different sizes from 150 mm to 600 mm and found that the compressive strength decreased with the increase of cube size; Mohammed et al. (2020) completely redesigned the concrete mixture based on the maximum size of coarse aggregate and selected different types of mixtures for experimental comparison to research the impact of maximum aggregate size on the strength of normal and high-strength concrete and it was spotted that the compressive strength increased with the increase in the maximum size of coarse aggregate; based on the results obtained from experimental studies, Saouma et al. (1991) and Li et al. (2004) spotted that the tensile strength of dam concrete decreases with increasing aggregate size; Rao et al. (2016) conducted a study to investigate the influence of aggregate particle size on the mechanical property of roller compacted concrete through the full-graded and wet sieve method test to comprehensively explore the impact of coarse aggregate’s grain size. The effect of coarse aggregate particle on the stability of roller compacted concrete in dams construction was also examined. The study provided technical support for the application of full gradation roller compacted concrete in practical engineering. It found that as the content of large-sized aggregates in full gradation concrete specimens increased, the air content of the concrete decreased, thereby improving the compressive strength, but larger maximum aggregate size resulted in poorer impermeability of concrete; Zhang et al. (2020) mixed different contents of macadam into four graded roller compacted concrete with a maximum grain size of 120 mm. They carried out mechanical properties and freeze-thaw cycles tests, and based on the test data, established a quantitative relationship between the gravel content and various mechanical properties, as well as the degree of damage, and developed a freeze-thaw damage model; Yang et al. (2016) found in the experiment that the reduction in the maximum particle size of macadam in fully graded concrete slightly reduces its compressive strength but slightly increases its tensile strength; Research into the microstructure of four graded roller compacted concrete (He et al. 2018) has shown that larger-size aggregates lead to more free water being adsorbed, which can have an effect on cement hydration as well as porosity, and then has a major impact on mechanical properties of concrete.
The compaction quality of roller compacted concrete is one of the key factors affecting its performance, and friction is generated in the aggregates during compaction, so the performance of roller compacted concrete has a close relationship with the aggregates used, and at the same time, it is also related to the relative compaction of vibration rolling of concrete, and the construction parameters and the number of times of rolling during compaction affect the relative compaction of concrete (Aghaeipour et al. 2020) , and controlling the compaction quality of layers is the key to ensuring the quality of the project.According to the development and research results of early roller compacted concrete(Hansen and Reinhardt 2000), the crucial points impacting bonding strength of interlamination of roller compacted concrete are summarized, including the impact of the compaction effect of the upper layer of roller compacted concrete on the interlayer adhesive force: the upper layer of compacted concrete will reduce the concrete void ratio at the layer, forming a good bond, when the rolling is not compacted or the aggregate separation at the layer, it will make the concrete void ratio at the level increase significantly, leading to a reduction in the bonding strength of interlamination. When compaction is not compacted or aggregate separation occurs at the layer, the void ratio of concrete at the layer will increase significantly, leading to a reduction in interlayer adhesive force. Insufficient or excessive compaction will lead to deterioration of the concrete performance, which will have an impact on the integral stability or anti-seepage effect of the dam, and affect the healthy operation of the dam; the current research on rolling parameters includes the role of different rolling parameters in vibratory compacted (VC) (Kokubu et al. 1996), the monitoring method of rolling parameters(Zhong et al. 2009; Zhong et al. 2011)and the compaction quality control technology based on rolling parameters (Liu et al. 2012). Liu et al. (Liu et al. 2015) used the unit compaction energy index to quantify the quality of roller compacted concrete dams; Godoi et al. (2019) improved the technique of using conventional X-ray imaging to detect the compaction degree of compacted layers. Compared with conventional concrete, roller compacted concrete requires more aggregates for compaction and consolidation. Both the degree of compaction and the number of rolling vibrations needed during construction are impacted (Harrington et al. 2010; Delatte et al. 2006); Xu et al. (2022) analyzed the compaction mechanism and established a compaction quality control system based on the results of on-site experiments, obtained economic and efficient compaction quality parameters to meet the construction quality control and rapid mechanized construction, and verified their reliability; Amer et al. (2004) Compaction of roller compacted concrete mixtures to different densities using the rotary compactor and experimental study on the improvement of roller compacted concrete mix proportion using rotary compactor; Williams et al. (2013) and Amer et al. (2003) compared the compaction densities and mechanical properties of roller compacted concrete compacted using the Proctor compaction methods with those compacted using gyratory compaction method, and found that the gyratory compaction method produced significantly higher densities at higher water contents; Selvam et al. (2023) in a comprehensive investigation found that the main factors affecting aggregate distribution are the ratio of aggregates to mortar, particle spacing, and compaction method. The compaction method plays a crucial role in the formation of the internal structure of roller compacted concrete. After conducting compaction tests on the samples using multiple compaction methods, it was found that the maximum density and compressive strength in the samples were compacted using the vibrating hammer; Şengün et al. (2018; 2019) used four laboratory compaction methods for the compaction of roller compacted concrete of two mix proportions and found that as the VeBe time increased, the difference in compaction coefficients obtained from specimens compacted using different compaction methods increased. Using a vibrating hammer for compaction can make specimens with low cement content have higher density and strength values. The strength and density of samples compacted using a rotary compactor are more similar to the actual engineering situation; Zhao et al. (2021) modeled the change of compaction energy density with compaction degree, quantified the compaction energy density and proposed a new method for compaction program development and adjustment of the number of rolling times. Fracture toughness (KIC and CTODC) is an important parameter in determining the performance of ultra-high arch dams; Sengun et al. (2021) designed seven different mixtures to study the fracture characteristics of roller compacted concrete in their experiment. The experimental results showed that as the maximum aggregate particle size and compaction coefficient of aggregates increased, the fracture parameters also increased.
With the development of dam building technology in recent years, four-graded roller compacted concrete has gradually been considered and applied in actual projects, its research and use have imcreased the maximum particle size of aggregate, saved water consumption, further reduced the amount of mortar and cementitious materials of roller compacted concrete (Golewski and Sadowski, 2016), improved the crack resistance performance, and fully utilized its technical and economic advantages (Lindquist et al. 2014). However, due to the increase in aggregate particle size, it may cause problems such as aggregate separation or internal defects in concrete, and may also affect the compaction effect of vibratory milling and thus affect the structural impermeability of the dam and the performance of the mix (Hashemi et al. 2018). Roller compacted concrete requires proper compaction methods to achieve the required engineering properties, improved compaction increases the load carrying capacity and thus the service life of the project (Selvam et al. 2023). The dense accumulation of aggregates in roller compacted concrete mixture helps to achieve higher compressive strengths (Selvam et al. 2022). The use of a four-graded roller compacted concrete instead of a three-stage roller compacted concrete leads to a reduction in the dosage of cementitious materials, and a reduction in the hydration temperature rise is reduced, which can effectively simplify the temperature control measures, increase the paving layer thickness in construction, reduce the level, improve the construction speed and productivity, and give full play to the technical and economic advantages of continuous pouring and rapid rise of the roller compacted concrete (2016). However, there are not many researches on the four-graded distribution of roller compacted concrete, and many aspects of the technical information have certain limitations or are almost blank. The water-cement ratio and aggregate proportion, as well as the choice of construction technology, all affect the performance of the roller compacted concrete. This paper analyzes the above problems experimentally to provide a reference for the choice of water consumption, sand rate, coarse aggregate proportion and construction technology of four-graded roller compacted concrete.