Engineering topics

Mechtcherine, Viktor

Publications and source records attributed to Mechtcherine, Viktor.

3 records

DOE OSTI2023

Using micro-XRF to characterize chloride ingress through cold joints in 3D printed concrete

Digital fabrication methods with concrete have been rapidly developing, with many problems related to component production and material control being solved in recent years. These processes produce inherently layered cementitious components that are anisotropic, and in many cases, produces a weak interface between layers, which are generally referred to as cold joints. While material strength at these interfaces has been well studied in recent years, durability has received less attention, even though cold joints can function as channels for aggressive agents, such as chlorides. This work presents a method using micro-X-ray fluorescence (μXRF) to image chloride ingress into layer interfaces of 3D printed fine-grained concrete specimens produced with varying layer deposition time intervals, and also compares it to neutron imaging of moisture uptake. The results show that cold joints formed after a 1 day time interval are highly susceptible to chloride ingress, and that curing conditions play a major role in how quickly interfacial transport can take place. The μXRF method is also shown to be useful for study of transport of chlorides in cold joints, due to its spatial resolution and direct analysis of an aggressive species of interest.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Modelling the development of capillary pressure in freshly 3D-printed concrete elements

3D concrete printing is a promising technology recently developed to automate construction. Since no formwork is used in this technology to support and protect fresh concrete, there are two aspects which considerably accelerate the development of capillary pressure in 3D-printed concrete in comparison to conventionally placed concrete: i) high stiffness of 3D-printed needed to provide sufficient buildability, and ii) very early and fast evaporation of pore water. Accelerated development of capillary pressure may lead to severe plastic shrinkage cracking in 3D-printed elements and, hence, need to be mitigated. This investigation aims at providing a poromechanical model for capillary pressure development in 3D-printed elements. To simulate the development of capillary pressure and plastic shrinkage, environmental factors, material properties, and element geometry need to be considered as a whole. The model inputs – coefficient of permeability, static bulk modulus, air entry pressure and chemical shrinkage rate – were determined experimentally. The model was validated for two fine-grained concretes. Both 3D-printed materials yielded faster capillary pressure increase in comparison to cast concrete, while partial substitution of cement with silica fume further accelerated the capillary pressure development. Furthermore, due to the lower permeability of the mixture containing silica fume, the gradient of capillary pressure between 3D-printed layers increased, as did the gradient of plastic shrinkage.

36 MATERIALS SCIENCE↗

DOE OSTI2021

On the use of limestone calcined clay cement (LC3) in high-strength strain-hardening cement-based composites (HS-SHCC)

Highlights: • Use of LC{sup 3} slightly reduces flowability and shortens the setting time of fresh matrices. • Highly polymerized C-A-S-H gel and abundant ettringite benefit flexural strength of LC{sup 3}-matrices. • Use of LC{sup 3} enhances the bond strength between fiber and high-strength matrix. • LC{sup 3}-based HS-SHCC yields similar flexural performance as the composite with Portland cement. High-strength strain-hardening cement-based composites (HS-SHCC) demonstrate excellent mechanical and durability properties. However, high cement content typical to HS-SHCC results not only in high carbon footprint, but also in excessive hydration heat and severe autogenous shrinkage. In this investigation, Limestone Calcined Clay Cement (LC{sup 3}) was used to produce sustainable HS-SHCC. The LC{sup 3} substitution resulted in higher energy consumption during mixing and in shorter setting times of the fresh, plain matrices. Although the LC{sup 3} substitution slightly reduced the compressive strength, the formation of highly polymerized C-A-S-H gel and abundant ettringite benefited the flexural strength of the plain matrices. Additionally, single-fiber pullout experiments showed that the use of LC{sup 3} led to increased fiber-matrix bond strength and pullout energy. Finally, the replacement of Portland cement by LC{sup 3} resulted in HS-SHCC with similar mechanical performance to the reference composite, indicating a high potential for using LC{sup 3} in high-performance cement-based composites.

36 MATERIALS SCIENCE↗