Comprehensive design methodology for 3D printing mortars

Digital technologies and automation processes are boosting additive manufacturing of cementitious materials, known as 3D printing of mortars and concretes, to build prefabricated and on-site concrete structures, taking advantage of increasing productivity and geometric freedom and of reducing manpower, waste and formwork. However, in additional to the mechanical and time-dependent performance, the following requirements must be assured in fresh state to allow the 3D printing process: extrudability, shape retention, constructability and open time. The global interest by this technology justifies the large number of works that are being nowadays developed. However, despite the successive progress, the published researches are mainly based on empiric material formulation, with high cement/aggregate ratios and consequently with high content of Portland cement, which contributes to prejudice the carbon footprint and the sustainability of the solution. The present research aimed to develop a design methodology for eco-efficient 3D printing mixtures, with reduced cement content and consequently lower cost effective. An experimental program was firstly developed to quantify the influence of the variation of the following parameters on the abovementioned fresh requirements: grade of cement strength; binder/aggregate ratio; aggregate size proportioning, including filler; w/c ratio and; superplasticizer type and proportion. The results analysis allowed to achieve high correlations between those parameters and the properties that affect the 3D printing requirements. The comprehensive developed methodology, based on those correlations, was proven to reliably allow designing eco-efficient mixtures, with binder/aggregate ratio of 1/2 to 1/2.5 that fulfil the necessary requirements, being tested and also validated in 3D printing equipment.