Research On The Evaluation Of Strength For Normal Concrete Perforated Brick In Existing Masonry Structures By Rebound Method

Rebound is a method to estimate the compressive strength of concrete and bricks by using a spring-driven hammer to hit the surface of materials and measure the rebound value (the ratio of the initial length of the rebound from the spring) as a strength parameter. As one of widely used nondestructive testing,rebound has fast detection speed, easy to carry, characterized by simple operation and nondestructive.Fired brick rebound method test the compressive strength of masonry structure is used more and more common, but has not been applied in non-fired brick.In order to protect the environment,save energy and develop light-weight,high strength and energy saving wall materials,concrete perforated brick become the first choice from place to place,however,a concrete perforated brick rebound strength formula has not been in relevant standard.Therefore, it is necessary to establish a unified rebound strength curve for concrete perforated brick in masonry structure.This thesis used the method of mathematical statistics and regression analysis to establish unified rebound strength curve for concrete perforated brick in masonry structure through the experimental study and data analysis.This thesis main contents are as follows:(l)The research processes, developments and characteristics of the concrete perforated brick has been introduced.The basic principles and key influencing factors of rebound method to detect the concrete perforated brick strength in masonry are summarized.Based on the test of 110 bricks chosen from walls by Sichuan Institute of Building Research and Jiangsu Institute of Building Research, the differences of the rebound value for concrete perforated brick ribbed and without ribbed position has been investigated in this research.(2)The influences of different mortar strength to rebound value was studied in Jiangsu Institute of Building Research by three experimental masonry wall.(3)In addition,the influences of different vertical pressure, and test methods to the rebound value are studied in the experiment of 12 masonry specimens by Hunan University.(4)Using Origin9.0 software for curve fitting:The rebound test adopted ZC3-A concrete rebound hammer and compressive strength test to the 80 concrete perforated brick which made in structure of Hunan university laboratory,received 80 groups of rebound value-compressive strength test data.The data were divided into 22 groups with the group interval of 0.5. The average value of rebound value and compressive strength in each group were calculated.As well as,using ZC4 brick rebound hammer and compressive strength test to the 6 concrete perforated brick masonry specimens and three walls which were made in structure of Hunan university laboratory and Jiangsu Institute of Building Research.Received 80 groups of rebound value compressive strength test data and divided into 20 groups. According to the principle of least squares regression analysis with two kinds of rebound hammer data,then got ZC4 brick rebound hammer parabola function expression for concrete perforated brick rebound strength formula.