Keywords

1 Introduction

Due to the rapid development of the transportation industry, road diseases are on the rise. Joints, being one of the weakest points in prefabricated pavement structure, exhibit varying load transfer capacities due to different structural forms. As a result, numerous scholars both domestically and internationally have conducted research on the load transfer capacity of cement concrete pavement joints [1]. Nowadays, the research on seam load transmission capacity mainly revolves around the design of the force transmission rod, and with the widespread use of the joint transmission rod, foreign scholars have successively appeared the joint design theory of the force transmission rod. Swati [2] analyzed the relationship between load, pavement performance and joint load transfer capacity by finite element software. Zhao Fangon [3] et al. studied the stress distribution of transverse joints under the state of pavement de-hollowing by establishing a three-dimensional finite element model, and analyzed the influence of force transmission rod spacing and cross-sectional size on joint load transfer. Tian Zhichang [4] used numerical analysis methods to analyze the relationship between the load stress in the cement pavement and the size of the plate, discussed the influence of the size of the groove on the tensile stress, shear stress distribution and deflection transfer effect at the joint, and proposed the relevant optimization scheme. Zhang Xin [5] et al. optimized the design of different sizes of joints of steel fiber road panels. At present, most of the research on joint load transfer capacity at home and abroad is aimed at ordinary concrete [6, 7]. In this paper, the load transfer capacity of the prefabricated steel fiber concrete pavement is analyzed by designing lap joints and groove joints, and the joint load transfer capacity is evaluated by the stress value.

2 Test Overview

2.1 Specimen Design

  1. (1)

    Raw materials and mix ratio

    In order to improve the durability and service cycle of prefabricated steel fiber road panels, P.0.42.5 grade ordinary Portland cement was used in the test, and the particle size range of coarse aggregate was 5.0 mm ~ 19.00 mm. Road steel fiber has requirements for flatness, fiber distribution uniformity, etc., so the end hook steel fiber is selected. The coarse aggregate uses 5.0 mm ~ 19.00 mm crushed stone as the coarse aggregate of the test, in order to ensure the reinforcement and toughening of concrete, the steel fiber content is controlled at 1.5%. And the same volume is used instead of coarse and fine aggregate to calculate the steel fiber mix ratio, the formula is as follows [8].

    $$ {\text{S}}_P { = }\frac{S_0 }{{G_0 + S_0 }} $$
    (1)
    $$ k = \frac{S_0 }{{G_{0} }} = \frac{S_P }{{1 - S_P }} \, $$
    (2)
    $$ V_f = \frac{\Delta S_0 }{{\rho_s }} $$
    (3)
    $$ k = \frac{\Delta S_0 }{{\Delta G_0 }} $$
    (4)

    where: \(G_0\) and \(S_{0}\) are the amount of 1 m3 matrix concrete stones and sand, respectively, in kilograms (kg);

    • k is the proportion of the amount of sand and stone;

    • Vf is the volume percentage of steel fiber in steel fiber concrete;

    • \(\Delta S_0\) and \(\Delta G_0\) are the amounts used by steel fibers to replace sand and stone.

The mix ratio of steel fiber reinforced concrete is shown in Table 1 below.

Table 1. Steel fiber concrete mix ratio
Full size table
  1. (2)

    Test board design and manufacture

    In this experiment, a total of 3 prefabricated steel fiber concrete pavement slabs were designed, and the size of the specimens was 500 mm × 500 mm × 200 mm. Before concrete is poured, templates need to be made according to the size of the specimens. After the completion of the template to ensure the accuracy of the shape and size of the structure, so the selection of steel mold production, the test design of two different joints of SFPCP, the joint form is mainly rectangular groove joint and lap joint two forms, the joint size as shown in Fig. 1 below.

    Fig. 1.
    figure 1

    Joint construction drawing (unit: mm)

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When the prefabricated steel fiber concrete specimen is made, the steel fiber is dispersed into the mixer to ensure that the steel fiber is evenly dispersed in the plain concrete, and the production and maintenance of the test piece are in accordance with the “Test Method Standard for Physical and Mechanical Properties of Concrete” (GB/T50081-2019) [9] and the “Test Method Standard for Fiber Concrete” (CECS 13-2009) [10].

  1. (3)

    Test block curing

    The SFPCP board is maintained by watering at room temperature, watering every 3 h until the mold is removed, and the mold is removed after 24 h of maintenance. After demoulding, the SFPCP pavement board should be covered with moisturizing film and watered every 6 h to give full play to the hydration reaction of concrete in the board.

2.2 Loading Scheme and Measuring Point Arrangement

  1. (1)

    measuring point layout A total of 8 measuring points are arranged on the test board, among which 2 displacement sensors (Linear Variable Differential Transformer-LVDT) are set up on the groove joint and the lap joint respectively, which are used to record the real bending value of the joint during the loading process. The two adjacent plates are installed with a strain gauge at the joint (1# and 2# are the strain gauge at the groove joint, 3# and 4# are the strain gauge at the lap joint), which is used to measure the strain at the joint. The load arrangement diagram is shown in Fig. 2, and the measuring point arrangement diagram is shown in Fig. 3.

Fig. 2.
figure 2

Test load layout drawing

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Fig. 3.
figure 3

Survey point layout drawing

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  1. (2)

    Test device and loading method

① Test device in this test, a 500 kN rigid reaction frame is used, and the loading speed and data collection of the 500 kN hydraulic jack in the middle span are controlled by a hydraulic operating platform. The detailed equipment diagram is shown in Fig. 4.

Fig. 4.
figure 4

Test equipment diagram

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② Loading method before loading, make the jack and the plate in just contact state. The load form of the test board is step by step loading, using 0.5 kN/s to load, stop loading when the load to 23 kN, stop loading console automatically unloaded, in this test did not carry out destructive test and limit loading. After the start of the test, data is collected at a frequency of 1 s during the loading process, and the load and displacement values are automatically recorded. The test device is shown in Fig. 5.

Fig. 5.
figure 5

Test setup and fact-finding diagram

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3 Analysis of Test Results

  1. (1)

    Time-deflection time-history curve

The bending curve of the SFPCP plate joint with time is shown in Fig. 6:

Fig. 6.
figure 6

Deflection-time history curve

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From Fig. 6, it can be seen that whether the deflection value of the groove joint or the lap joint gradually increases during the loading process, the deflection changes with time is not increased in a certain proportion, but appears up and down in a state of fluctuation, and it can be seen from the analysis that when pouring the road panel, due to the small size of the joint, the vibration is not particularly sufficient. Through comparison, it is found that with the increasing time, the deflection of both seams is increasing and both are negative, indicating that the seam displacement is vertical upward. The change trend of the two seams is similar, the difference is that when the time has passed 25 s, the degree of change of the deflection value of the groove seam is greater than that of the lap seam, and it is almost a straight downward trend, while the lap joint will also fluctuate up and down, indicating that the lap joint is better than the groove joint when considering the deflection value factor of the road deck joint.

  1. (2)

    Strain-time history curve

In the course of the test, two joints of the intermediate plate are arranged with 2 strain measuring points, and strain gauges are arranged on both sides of the plate at the corresponding positions with the intermediate plate joints to measure the strain at the joints. The time-history curve of the test plate is shown in Fig. 7.

Fig. 7.
figure 7

Groove seam strain-time history diagram

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By comparing Fig. 7 (a), (b), (c) and (d) respectively, it can be seen that whether it is a groove joint or a lap joint, the strain value changes very little in the first 5 s, and from the curve graph, the strain value changes almost straight line; The maximum strain value at both ends of the groove joint appeared at different times, the maximum strain value at the left end of the groove seam appeared after loading 26 s, and the maximum strain value at the right end appeared after loading 37 s. The strain value of the lap joint is also very small 5 s before loading, but the degree of change at both ends of the seam is very large, indicating that the two ends of the joint are compressive strain at this time, and the seam strain suddenly increases. The left end of the lap joint has always been compressive strain, and although the right end of the lap joint has tensile and compressive strain at the same time, it has more time in compressive strain.

4 Summary

Through the joint bending strain conduction test of SFPCP plate, the main conclusions are as follows:

  1. (1)

    From the seam deflection-time history change curve, it can be seen that the deflection value of the groove joint or the lap joint maintains a downward trend during the loading process, and the deflection value fluctuates up and down with time, indicating that the steel fiber has a certain inhibitory effect on the deflection of the joint. When considering the deflection value of the road deck joint, lap joint joints are recommended.

  2. (2)

    From the strain-time history curve of the joint, it can be seen that the strain change law at both ends of the groove seam is similar, and the tensile and compressive strain time at both ends of the seam is relatively average, while the left end of the lap joint is always in a compressed state, and the right end is mostly in a tensile state.

Project Funding

  1. (1)

    2023 Chongqing Higher Education Teaching Reform Research Project (Grant Nos: 233447) and 2023 Chongqing University of Science and Technology Undergraduate Education Teaching Reform Research Project (Grant Nos:202342); 2. 2023 Chongqing Construction Science and Technology Plan Project (Funded Project: 18) “Research and Demonstration of Key Technologies of Prefabricated Steel Fiber Concrete Pavement Panel”.