再生细骨料和砖粉双掺对3D打印混凝土性能的影响

Effect of Recycled Fine Aggregate and Clay Brick Powder on Properties of3D Printed Concrete

为减少3D打印混凝土中天然骨料及胶凝材料的用量,本文采用再生混凝土细骨料替代部分天然细骨料,砖粉替代部分水泥,首先开展单掺再生细骨料(取代率为0、25%、50%、75%和100%)、单掺砖粉(取代率为0、5%、10%、15%、20%和30%)和两者双掺的现浇混凝土的流动性和抗压强度试验,以获得再生细骨料和砖粉的适宜取代率;然后探究50%再生细骨料和10%砖粉双掺及配合比调整方式(附加水、提高减水剂用量)对3D打印混凝土拌合物性能及硬化后力学性能的影响。试验结果表明,当再生细骨料的掺量不超过50%时,现浇混凝土抗压强度降低幅度在10%以内;随着砖粉掺量从0增加到30%,现浇混凝土抗压强度总体呈现先增后减、再稍有增加的趋势,当砖粉掺量为10%时,混凝土抗压强度最高;相比于单掺50%再生细骨料的混凝土,50%再生细骨料和10%砖粉双掺时混凝土强度有所增加,而流动性基本不变。对于3D打印混凝土,同时掺入50%再生细骨料和10%砖粉,并采用添加附加水的方式保持3D打印混凝土初始扩展度不变,会使得混凝土的可建造性提高,但坍落度、开放时间、抗压和劈裂抗拉强度降低,强度各向异性加剧;而提高减水剂用量不仅能显著提升3D打印混凝土的流动性能、开放时间和抗压强度,还能降低打印试件的强度各向异性。

In order to reduce the amount of natural aggregates and cementitious material in 3D printed concrete,this study used recycled fine aggregate(RFA)to partially replace natural fine aggregate and clay brick powder(CBP)to replace cement.The fluidity and compressive strength test of cast-in-situ concretes with RFA only(0,25%,50%,75%and 100%replacement ratio),with CBP only(0,5%,10%,15%,20%and 30%replacement ratio)and with both of them were firstly carried out to obtain the optimal replacement ratio of RFA and CBP.Then,it investigated the effect of the addition of 50%RFA and 10%CBP and the corresponding mix proportion adjustment methods(adding extra water and increasing water reducer dosage)on the fresh and harden properties of 3D printed concrete.The test results indicate that the decreasing amplitude of the compressive strength of cast-in-situ concrete is within 10%when the replacement ratio of RFA is less than 50%.With the increase of CBP replacement ratio from 0 to 30%,the compressive strength of cast-in-situ concrete increases first,then decreases and then slightly increases.The specimen with CBP content of 10%exhibits the highest compressive strength.Compared to the concrete with 50%RFA only,the concrete with 50%RFA and 10%CBP has higher strength,while the fluidity is almost kept unchanged.For 3D printed concrete,the addition of 50%recycled fine aggregate and 10%brick powder and additional water can keep the initial expansion of 3D printed concrete unchanged and improve the buildability of concrete,but it can decrease the slump,opening time,compressive and split tensile strength and increase intensity anisotropy.However,increasing water reducer dosage in the mixture can not only significantly improve the fluidity,opening time and compressive strength of 3D printed concrete,but also reduce the intensity anisotropy.