Heat Release during 3d-Printable Materials Setting and Hardening

The paper presents the experimental data on the cement effect typeon the effects of heat generation during the 3D-printable cement materials’setting and hardening. Materials made on the basis of cements CEMI 42.5 RandCEMI 52.5 R, differing in phase contentC3Ain combination with viscosity modifiers of various compositions,have been studied. To control setting kinetics, a penetrometer test was used, hardening kinetics was evaluated by testing the samples for compressive strength after 1, 3, 7, 14, 28 days of hardening. It was found that the useof CEMI 52.5 Rhigh in compositionC3Acauses a significant heating of the mixture already after its setting, which is not observed when using ordinary CEMI 42.5R. The combination of a highly active aluminosilicate modifier with high-strength cement causes a technologically unacceptable reduction in the setting time and open time of mixtures.

Влияние добавок модификаторов вязкости на реологическое поведение цементных систем для 3D-печати

Представлены результаты экспериментальных исследований реологического поведения модельных цементных систем как матриц смесей для 3D-печати. В проведенных экспериментах использованы: для изучения реологического поведения – сдавливающие тесты; для оценки показателя пластичности, характеризующего способность смесей сохранять агрегативную устойчивость в процессе экструзии, – сдавливающий тест с постоянной скоростью деформирования; для оценки формоустойчивости – сдавливающий тест с постоянной скоростью нагружения, по результатам которых найдены значения структурной и пластической прочности, пластических деформаций цементных систем, характеризующие их способность сохранять форму при действии возрастающих сжимающих напряжений в процессе печати. Получены количественные данные о влиянии видов и дозировок неорганических модификаторов вязкости различного химико-минералогического состава и дисперсности на пластичность и формоустойчивость цементных смесей. Установлено, что для рассмотренных составов наиболее эффективными модификаторами вязкости являются тонкодисперсные метакаолин и каолин со средним размером частиц 5 мкм. Регулирование вязкопластических свойств и агрегативной устойчивости цементных систем определяется изменением свойств дисперсионной среды в гетерогенной системе «цемент–вода». Определены рациональные дозировки данных модификаторов, при которых обеспечиваются критериальные значения показателей пластичности для процессов 3D-печати, структурной прочности и деформативности при действии нагрузки. Ключевые слова: 3D-печать, цементная смесь, модификатор вязкости, реологическое поведение, пластичность, формоустойчивость. The results of experimental studies of the rheological characteristics of cement pastes as a matrix of 3D-printable mixtures are presented. The squeezing tests were used to evaluate the rheological behavior. To evaluate the plasticity, which characterizes the ability of 3D-printable mixtures to maintain aggregate stability during the extrusion process, the squeezing test with a constant deformation rate was used. To evaluate the form stability a squeezing test with a constant loading speed was used. As a result, the structural and plastic strength, plastic deformations of fresh cement pastes were estimated as criteria of their ability to maintain shape under compressive pressure during the printing process. Quantitate data on influence of types and dosages of inorganic viscosity modifiers with various chemical and mineralogical composition and sizeparticles on the plasticity and form stability of cement pastes was obtained. It was found that the most effective viscosity modifiers are fine-dispersed metakaolin and kaolin with an average size-particle of 5 μm. As a result of using the most effective viscosity modifiers, adjustment of viscous-plastic properties and aggregate stability of cement pastes can be made by modifying the properties of the dispersion liquid in the heterogeneous "cement–water" system. Reasonable proportions of these modifiers have been obtained, which ensures plasticity, maximum structural strength and minimum deformability of 3D-printable mixtures under load. Keywords: 3D-printing, cement paste, viscosity modifier, rheological behavior, plasticity, form stability.

Fluid Effects on Mechanical Efficiency of Hydraulic Pumps: Dynamometer Measurements and Molecular Simulations

The mechanical efficiency of hydraulic pumps is affected by the viscosity of the hydraulic fluid. Viscosity modifiers that thicken the fluid, therefore, play an important role in efficiency. Viscosity modifiers are believed to improve the mechanical efficiency of hydraulic systems partially by enabling formulation with lower molecular weight base oils. Here, this concept was directly tested in a pump dynamometer using mixtures of low traction synthetic poly(alphaolefin) base oils, bis(2-ethylhexyl) adipate ester, and poly(isobutylene). Lower viscosity fluids directly correlated to better mechanical efficiency but decreasing the viscosity of the synthetic base oil by adding viscosity modifier did not have the same effect. However, molecular dynamics simulations showed that solution viscosity was directly correlated to elongation of the polymer under shear which, together with calculations of the critical shear rate range in a pump, suggested ways of designing viscosity modifiers to achieve a specific viscosity profile that maximizes mechanical efficiency.