Academic Journal of Science and Technology ISSN: 2771-3032 | Vol. 10, No. 1, 2024 28 Experimental Study on Optimizing Grouting Material Ratio for Rebar Sleeve Connections Ziqi Wang School of Environment and Architecture, University of Shanghai for Science and Technology, Shanghai 200093, China Abstract: In response to the inadequate performance reliability of existing prefabricated sleeve grouting materials, this study used an orthogonal experimental design method to prepare 16 sets of grouting materials based on C52.5 cement and ordinary river sand, with different water-cement ratios and varying amounts of additives including silica fume, defoamers, water reducers, and expansive agents. The effects of silica fume, defoamers, water reducers, expansive agent dosage, and water-cement ratio on the compressive strength, vertical expansion rate, and fluidity of the grouting material were studied. Based on the experimental results and comprehensive analysis, a formulation for high-performance grouting material with high reliability was determined, providing a greater safety margin for practical engineering applications. Keywords: Prefabricated construction; High-performance sleeve grouting material; Orthogonal experimental design. 1. Introduction A With the rapid progress of urbanization and continuous updates in construction technology, prefabricated construction [1] has seen significant development. Promoted vigorously in various countries and especially in the core areas of large cities, prefabricated construction methods have become mainstream. In prefabricated construction, the most important and challenging aspect is the connection method and reliability of prefabricated components. The current mainstream construction methods mainly include dry connection and wet connection [2], with dry connections like bolted and mechanical connections, and wet connections like dovetail anchorage and grout sleeve connections. Among these, grout sleeve connections, due to their high reliability and controllable construction process, are the most widely used connection method for prefabricated components. In grout sleeve connection technology, the work performance of grouting material is a critical guarantee for connection performance and reliability, holding significant research significance. Many scholars have studied the structural performance of steel sleeve grout connections [3-6]. However, the grouting materials commonly used in engineering projects are prefabricated materials produced by specialized factories, with basic performance only meeting the lower limits of specifications. Given the practical deviations in construction, the reserved safety margins often fail to meet the engineering requirements. In this study, 16 different grouting materials were prepared through experiments by the author, and various performance tests were conducted on standard specimens, followed by result analysis. 2. Experimental Design 2.1. Materials The grouting materials used in this study were prepared by the author based on the requirements stipulated in JG/T408- 2019 “Cementitious grout for sleeve of rebar splicing,” [7] using C52.5 cement and ordinary river sand as the base. Five factors were considered for the study, including silica fume, polyether-based defoamer agent, polycarboxylate-based water reducing agent, plasticizing expansive agent, and water-cement ratio. The properties of the additive materials are presented in Table 1, and the appearance of the materials is shown in Figure 1. Table 1. Material properties of grouting materials Component Properties P.O52.5 Cement Compressive Strength at 3 days: 32.2MPa, Specific Surface Area: 382m2/kg Silica fume Dark grey powder, SiO2 content: 91.6%, Average Particle Size: 0.1~0.3μm, Specific Surface Area: 20~28m2/g River sand Ordinary river sand: 10 mesh~20 mesh; 20 mesh~40 mesh; 40 mesh~60 mesh Polycarboxylate water reducing agent White powder, Recommended Dosage: 0.16~0.3% of cementitious materials Plastic expansive agent Light yellow powder, Specific Surface Area: 250m2/kg Polyether defoaming agent White powder, pH value: 6~8 Water Ordinary tap water 29 (a) Cement (b) Silica fume (c) River sand (d) Expansive agent (e) Defoaming agent (f) Water reducing agent Figure 1. Material appearance 2.2. Grouting material performance indicators and testing methods This study selected compressive strength, vertical expansion ratio, and fluidity as the key indicators of the performance of the grouting materials prepared for research and analysis. 2.2.1. Compressive strength In this experiment, the compressive strength was determined according to GB/T17671-2021 “The method of cement mortar strength (ISO method)” [8], as shown in Figure 2. Figure 2. Compressive strength test 2.2.2. Vertical expansion ratio and fluidity The vertical expansion ratio and fluidity of the mortar were determined using the contact type vertical expansion ratio measurement method and fluidity test method in the appendix of JG/T408-2019 “Cementitious grout for sleeve of rebar splicing,” as shown in Figures 3 and 4. Figure 1. Vertical expansion ratio test Figure 2. Fluidity test 30 3. Experimental Design This study used orthogonal experimental design for experimental planning. Orthogonal experimental design is a method that reduces the number of test groups and improves test efficiency while still ensuring a high degree of reliability in studying the impact of various factors on the target results and the optimal combination of factors. The silicon fume content, polyether defoamer content, polycarboxylate water reducing agent content, plastic expansive agent content, and water-cement ratio are selected as influencing factors, each with four levels as shown in Table 2. An orthogonal experiment is designed with 3d compressive strength, 3h vertical expansion rate, and initial fluidity as indicators. The L16(45) orthogonal table is used for the experimental design, and the measured results are filled in as shown in Table 3. Table 2. Level setting of orthogonal experiment factors (A) Silica fume /％ (B) Defoamer agent /‰ (C) water reducing agent /‰ (D) expansive agent /‰ (E) water-cement ratio 2.5(1) 0(1) 0(1) 0(1) 0.22(1) 5(2) 3(2) 3(2) 1(2) 0.25(2) 10(3) 6(3) 6(3) 2(3) 0.27(3) 12.5(4) 9(4) 9(4) 3(4) 0.3(4) Table 1. Orthogonal experimental table Test number Test factors Compressive strength /MPa Vertical expansion ratio /％ Fluidity /mm A B C D E 1 1 1 1 1 1 74 0.33 329 2 1 2 2 2 2 87 0.41 371 3 1 3 3 3 3 88 0.47 401 4 1 4 4 4 4 82 0.63 412 5 2 1 2 3 4 118 0.56 428 6 2 2 1 4 3 132 0.71 398 7 2 3 4 1 2 136 0.41 366 8 2 4 3 2 1 126 0.50 317 9 3 1 3 4 2 115 0.58 360 10 3 2 4 3 1 121 0.52 333 11 3 3 1 2 4 124 0.60 403 12 3 4 2 1 3 123 0.37 389 13 4 1 4 2 3 94 0.33 399 14 4 2 3 1 4 101 0.33 407 15 4 3 2 4 1 107 0.64 328 16 4 4 1 3 2 88 0.52 357 4. Data Analysis Range refers to the difference between the maximum and minimum values of measured indicators at different levels of each factor. A larger range indicates a greater impact of the factor. In this study, range analysis method was used to analyze the three indicators separately. Considering the influencing mechanisms of each factor and the importance of each indicator in practical engineering, a set of optimal factor combinations was determined. An indicator analysis table was created based on the experimental results, as shown in Tables 4 to 6. Table 4. Analysis table of compressive strength Analysis results A B C D E T1 332 401 418 434 428 T2 512 441 435 431 441 T3 483 455 424 415 437 T4 390 419 432 436 425 R 180 54 17 21 16 Primary and secondary order ABDCE Optimal combination A2B3C2D4E2 31 Table 5. Analysis table of vertical expansion ratio Analysis results A B C D E T1 1.84 1.80 2.16 1.44 1.99 T2 2.18 1.97 1.98 1.84 1.92 T3 2.07 2.12 1.88 2.07 1.88 T4 1.82 1.89 1.89 2.56 2.12 R 0.36 0.32 0.28 1.12 0.24 Primary and secondary order DABCE Optimal combination A2B3C1D4E4 Table 2. Analysis table of fluidity Analysis results A B C D E T1 1513 1516 1487 1491 1307 T2 1509 1509 1516 1490 1454 T3 1485 1498 1485 1519 1587 T4 1491 1475 1510 1498 1650 R 28 41 31 29 343 Primary and secondary order EBCDA Optimal combination A1B1C2D3E4 In the table, “Tn” represents the sum of measured values corresponding to the n-th category of factors, and “R” represents the range of these values. Factors with larger ranges have a greater impact on the indicator. Therefore, the order of factors from largest to smallest range determines their importance. The combination of factors corresponding to the optimal indicator values is considered the optimal combination. Based on the analysis of the three indicators, it is clear that there are prominent main factors influencing all three performance indicators. Therefore, in determining the mix ratio, the three key factors A2D4E4 can be first selected. Factors B and C, serving as additive components, do not have a dominant impact on the indicators. According to the analysis results, the combination of B3C2, which was found to be optimal for two out of the three indicators, can be considered for use. 5. Conclusion This study designed an orthogonal experimental plan and experimentally measured three important indicators: compressive strength, vertical expansion ratio, and fluidity. The study analyzed the impact of adding different amounts of silicon ash, air-entraining agent, water reducing agent, expansive agent, and adjusting the water-cement ratio on these three major indicators based on C52.5 cement and ordinary river sand. After comprehensively analyzing the degree of influence and effects, the study determined that the combination of A2B3C2D4E4 is the optimal one, providing a grouting material mix design with a higher safety margin for practical engineering applications. The following conclusions were drawn from the experimental work: 1) Compressive strength, vertical expansion rate, and fluidity are mainly influenced by the amount of silicon fume, vertical expansion rate, and water-cement ratio, which should be emphasized in practical engineering applications. 2) The grouting material mix design obtained in this study outperforms factory-prepared grouting materials in terms of performance, providing a more reliable safety margin for engineering practices and ensuring better connection effects for prefabricated components. 3) Due to the large amount of experimentation, there may be some experimental errors, and the actual utility of additives that did not play a dominant role in the three major performance indicators examined in this study was not significantly demonstrated. Future research could focus on analyzing these additive components using other performance indicators to reach a more comprehensive conclusion. 4) The orthogonal experimental method used in this study is concise and clear, making it a feasible method for pre- construction experiments by construction site engineers. However, future research should delve deeper into further studying and exploring the interactions between various factors. References [1] GUO Zhengxing, DONG Niancai, ZHU Zhangfeng. Development of Construction Technology of Precast Concrete Structure in Buildings [J]. Construction Technology, 2011, 40(11): 1-2+34. [2] WU di. Summary of the Research on the Connection Mode of the Assembled Building Node [J]. Chinese & Overseas Architecture, 2016(08): 150-151. [3] ZHENG YONGFENG, GUO ZHENGXING, ZHANG XIN. Effect of grout properties on bond behavior of grouted pipe splice [J]. KSCE Journal of Civil Engineering,2018,22( 8) : 2951-2960. [4] HENIN ELIYA,MOＲCOUS GEOＲGE. 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