Design,Preparation And Toughening Of Self-compacting Lightweight Aggregate Concrete

Self-compacting lightweight aggregate concrete(SCLC)which combines the excellent performance of self-compacting concrete(SCC)and lightweight aggregate concrete(LWAC)has been developed.In the placing process,it needs no additional mechanical vibration and can be compacted by relying only on its own weight.In addition,SCLC can reduce the foundation load and the size of the member section.As a result,it has a very broad application prospect nowadays as the height and span of buildings are increasing.The mix design of concrete is the most important aspect for concrete production and application.It is related to the workability,mechanical properties and durability of concrete mixture in service.At present,there is a lack of mix design method with strong applicability for SCLC.The SCLC mix design method based on SCC and empirical method cannot realize the quantitative calculation of raw material content.It is not clear whether the recommended ranges of key mix parameters in SCC specification is suitable for SCLC.SCLC solves the problems of heavy weight and vibration of normal weight concrete,but it does not solve the problems of high brittleness,easy cracking and low tensile strength of concrete.How to improve the toughness,tensile strength and crack resistance of SCLC is the key problem to be solved in the process of further popularization and application of SCLC.In order to develop a SCLC mix design method with universal applicability and scientific rationality,a SCLC mix design method based on the theory of mortar film thickness is proposed.The above mix design method is optimized and improved from the perspective of mortar performance.The mix design of SCLC is divided into self-compacting performance design based on the rheological properties of mortar and strength design based on the water-cement ratio rule of mortar.In order to avoid incomparability of test results caused by different rheometers,two methods for evaluating the rheological parameters of mortar are established,that is,Marsh method and mini-slump method.After that,the most suitable method is obtained by comparing these two methods.The steel fiber reinforced self-compacting lightweight aggregate concrete(SFRSCLC)is prepared based on the theory of paste film thickness and the combination method.The effect of steel fiber content on the workability and basic mechanical properties of SCLC is also investigated.Based on the comparative analysis of the suitability of JG/T 472-2015 method and ASTM C 1609 method for SFRSCLC flexural toughness evaluation,a new method is proposed.In order to reveal the mesoscopic bridging effect of fibers on the cracks,the slippage mechanism of fibers and the damage evolution process of the cracks,the damage characteristics of SFRSCLC under uniaxial compression are studied based on acoustic emission technology.The main conclusions of this paper are as follows:The SCLCs which meet the requirements of self-compacting performance design with a density grade of 1800 or 1900 and a strength higher than 50 MPa can be prepared by using the SCLC mixture design method based on the mortar film thickness theory.Compared with the Marsh method,the mini-slump method is an ideal method to measure the rheological parameters of mortar.The self-compacting performance design method based on the rheological properties of mortar and the strength design method based on the water-cement ratio rule of mortar can predict the workability and strength of SCLC.The content of cementitious material can be determined quantitatively by the mix design method of SFRSCLC based on the paste film thickness theory and combination method.The addition of fibers into SCLC can reduce the filling and passing abilities of the mixture,but can improve the segregation resistance.Compared with the improvement of compressive strength,the splitting tensile strength,flexural strength and post-cracking toughness of SCLC can be significantly improved due to the addition of steel fiber.The JG/T 472-2015 and ASTM C 1609 methods are not suitable for evaluating the flexural toughness of SFRSCLC with larger peak mid-span deflection.The new flexural toughness evaluation method can effectively measure the flexural toughness of SFRSCLC.The dominant frequency bands of SFRSCLC are mainly distributed in four ranges: 15~45 kHz,85~105 kHz,235~255 kHz and 285~320 kHz,which corresponds to the compression of pre-existing cracks or pores in concrete,the fracture failure of aggregate/paste interface reinforcement layer,the penetration fracture of aggregate and the cracking of mortar,respectively.