Conference Agenda

With the development and use of Alkali Activated Concretes (AACs), a more sustainable alternative to Portland Cement Concretes (PCCs), it is becoming ever more important to understand its mechanical behavior over time. Herein, tensile behavior of a slag-based AAC (S-AAC) was investigated on dog-bone shaped samples tested in direct tension and compared to a CEMIII/B-based concrete (S-PCC). Samples have been fog-cured for 28 days and successively exposed to 55% relative humidity and 20⁰C until testing, at testing ages 28 days, 3 months, 6 months and 1 year. Stress-strain behavior of S-AAC was characterized by a significantly lower tensile strength and elastic modulus than S-PCC. From 28 days to 3 months, both concretes showed a reduction in tensile strength, which partially recovered at 6 months. Interestingly, after partial recovery, both concretes showed reduced tensile strength at the age of 1 year. Stress-crack opening curves and development of characteristic length over time showed that, unlike S-PCC, S-AAC softens under drying, which might be an effect of shrinkage-induced microcracking in S-AAC.

3D printing of concrete presents the new challenge of anisotropy to an already heterogenous medium of concrete. The layer-wise mode of construction quintessential to the printing of concrete leaves interfaces which have different properties to that of the layer. These interfaces interact and interfere with crack propagation compared to monolithically cast specimens and contribute to differential properties of structural elements in different directions. This phenomenon is identified by performing 3-point bending tests on printed elements with different layer orientations and comparing the fracture energy in Mode I (G_f) and peak flexural stresses (𝜎_𝑓) of the printed concrete tested. Subsequently, ABAQUS model of 3-point bending tests are developed with different material properties of the interface elements and the layers which are validated against the experimental results. Upon parametrisation of the fracture energy and peak flexural stress values, it has been noted that the properties of the interface elements are categorised by the tests done with the loading direction parallel to the layer orientation.

Since the production of cement is very CO2-intensive alternative binders are on the rise. The reactivation of cement has proven to be possible. Attempts are being made to find out, how it can be used as a binder or clinker supplement. A problem to solve is that, so far, the mechanical strength is not as high as the one of the original binder. Reasons for that are a new chemical composition with a different variety of strength giving phases and the morphology of the reactivated grains. The new powder shows high inner porosity and a much bigger specific surface area. This work aims to increase the mechanical strength of reactivated cement by using two types of additives. First, milling agents that are added during the milling process. In this study ground blast furnace slag (GBFS), copper slag (CuS) and electric arc furnace slags (EOS) were used. Further additives are added during the mixing of cement and water. Microsilica (MS), concrete plasticizer, superplasticizer and retarder have been chosen. Parameters that were tested are compressive strength, porosity and fracture toughness. While GBFS gives the highest compressive strength, chemical admixtures increase the strength of reactivated cement paste as well. The fracture toughness is a stable value whereas porosity and strength vary for reactivated cement.

Geopolymer concrete (GPC) is gaining significant attention as an eco-friendly alternative to traditional plain cement concrete (PCC), primarily due to its lower carbon emissions and superior mechanical properties. Recent research highlights its enhanced performance in terms of compressive strength, acid resistance, water permeability, and heat resistance. However, the behavior of GPC under cyclic loading, which is critical for assessing its long-term durability, still needs to be explored. This study aims to provide a better understanding of the fatigue performance of GPC, contributing to the broader assessment of its suitability for long-term use in construction applications. In this work, the fatigue crack growth rate of GPC is investigated using experimental data obtained from threepoint bending tests. Beam specimens of GPC, with dimensions of 100 mm x 100 mm x 500 mm, are subjected to cyclic loading at a frequency of 1 Hz. The peak load applied during these cycles is 80% of the material’s flexural strength, with a stress ratio of 0.1. A statistical model is employed to fit the experimental data and predict crack propagation trends under repeated loading. The crack length (a) versus number of cycles of loading (N) is recorded for each test, and is used for statistically predicting the fatigue crack growth behavior of GPC. Size adjusted Paris’ law parameters are obtained, offering a mathematical representation of how cracks propagate in GPC under repeated loading. The proposed fatigue crack growth equation may be useful for predicting crack behavior in GPC, facilitating more informed decisions regarding its application in infrastructure projects.