Study On Uniaxial Compressive Behavior Of High Strength Lightweight Aggregate Concrete

As a green building material,the high strength lightweight concrete(HSLWC)has many advantages like high durability,good frost resistance,good insulation properties.But it shows more brittle behavior than normal weight concrete at the compared strength levels.Few investigations on its basic mechanical properties with fiber,especially the complete stress-strain relatinonships of HSLWC under uniaxial compression,are reported at aborad.And the current stress-strain model proposed by Chinese standardization is mainly based on the test data of low intensity in the 70 s and the 80 s.Therefore,the main objective of this paper is to study the mechanical properties of HSLWC under uniaxial compression and to propose a new model that can give a good represention of the behavior of unconfined stress-strain response.In this paper,Group one including three different strengths(i.e.,LC40,LC50,LC60)was designed to be tested,and Group two with three different volume fractions(i.e.,0.3%,0.6%,0.9%)of carbon fiber and(i.e.,0.3%,0.6%,0.9%)steel fiber respectively using LC60 as a stander was also designed.The aggregate used in all of the test specimens was 900 grade high strength crushed stone shale ceramsite.Then the mechanical properties of HSLWC under uniaxial compression were researched.The work was showed below:(1)The test of elastic modulus of HSLWC was carried out.The effects for elastic modulus were investigated when strength,fiber type and different volumes of the mixed fiber were changed.On the basis of the experiment,a large database of 842 experimental results of lightweight concrete elastic modulus is assembled through an extensive review of the literature.Then a new model to predict the elastic modulus is proposed.Results show that no significant changes in elastic modulus of HSLWC due to the addition of carbon fiber or steel fiber are observed and by comparing the experimental results of HSLWC with the model calculation results,the accuracy of proposed model is verified.(2)The test of complete stress-strain curve of HSLWC was carried out.The effects of strength,fiber type and the mixed amount of fiber for peak strain,ultimate strain,and its failure process were discussed and presented.On the basis of the experiment,the conversion of HSLWC between axial compressive strength and compressive strength is suggested by collecting 107 groups of domestic lightweight aggregate concrete axial compressive strength datum.Research shows that the peak strain and the ultimate strain will increase when strength is increasing.Using fiber will improve the peak strain and ultimate strain,and the increase is related to the type of fiber and volume fractions of fiber.Based on the energy absorption capacity,a large increase in toughness of HSLWC due to the addition of fiber is obversed.(3)A number of empirical models availiable in the literature of the complete strss-strain curve for unconfinend concrete under uniaxial compression are reviewed and studied using the experimental data of HSLWC.Based on the investigations,a new modified model is proposed to genergate the complete stress-strain relationships of HSLWC.The parameters for the ascending and descending branches are obtained.A regression analysis carried out on the test data of 150 groups of unconfinend lightweight aggregate concrete gives the realtionship between the strain at pesk stress and the concrete strength.(4)Based on the statistical distribution function and damage mechanics theory,the stochastic damage constitutive model of HSLWC is established.The model has been found to give a good represention of the actual stress-strain response and to reflect the damage mechanism of HSLWC.The study on the basic mechanical properties of HSLWC can further improve the domestic and foreign test datum,and it provides a experimental basis for revision of related standards of lightweight aggregate concrete in our country.These obversations also have great significances in guiding engineering practice and promoting the wide application in domestic engineering when the properties of this kind of concrete and the changes of it after adding fiber in it are known better.