Crystallizing Metal Shrinkage: Automation of High-Pressure Crystallization Control

The properties of bulk metal products are formed when molten metal transforms from an unstructured liquid into a solid crystal state. We suggest a new approach to the automation of the control over crystallized metal shrinkage compensation based on controlling the law of change in pressure applied to crystallizing metal through a program taking into account the transition process in the hydraulic system of the production equipment. We observed the increase in rigidity, durability, and pliability of В95-alloy samples as compared to cast aluminum alloys. The metal utilization rate can be increased up to 0.90 of the liquid metal volume.

Circulating Fluidized Bed Fly Ash Mixed Functional Cementitious Materials: Shrinkage Compensation of f-CaO, Autoclaved Hydration Characteristics and Environmental Performance

Circulating fluidized bed (CFB) fly ash is a by-product from CFB power generation, which is hard to utilize in cement because it contains f-CaO and SO3. This work aims to explore the mechanism of the shrinkage compensation of free-CaO (f-CaO) and the autoclaved hydration characteristics and environmental performance of CFB fly ash mixed cementitious materials (CMM). In this work, long-term volume stability of CMM is improved with the addition of CFBFA. These findings suggest that the compressive strength of sample CMM0.5 is the highest under both standard condition (67.21 MPa) and autoclaved condition (89.56 MPa). Meanwhile, the expansion rate (0.0207%) of sample CMM0.5 is the lowest, which proves the shrinkage compensation effect of f-CaO in CFBFA. The main hydration products of CMM0.5 are Ca2SiO4•H2O (C-S-H) gel, CaAl2Si2O7(OH)2•H2O (C-A-S-H) gel and Ca(OH)2. In addition, the high polymerization degree of [Si(Al)O4] and the densified microstructure are presented at the sample CMM0.5. The leaching results indicates that the heavy metals in CMM0.5 satisfies the WHO standards for drinking water due to physical encapsulation and charge balance. Therefore, this investigation provides a novel method of using CFB fly ash in cement.

RAPID ASSESSMENT OF POZZOLANIC ACTIVITY IN DETERMINING THE EFFECTIVENESS OF EXPANSIVE SULFO-ALUMINATE TYPE ADDITIVES ABSTRACT

Применение расширяющихся добавок на основе сульфоалюминатных композиций для модификации цементных систем позволяет не только компенсировать усадку, но в ряде случаев получить расширение и самонапряжение. На сегодняшний день рынок изобилует расширяющимися добавками на основе сульфоалюминатных композиций, представляющими собой как искусственно синтезированные материалы, так и механические смеси на основе метакаолина, глиноземистого цемента и гипса (цемент типа «М»). Выбор того либо иного вида добавки, а также ее дозировка назначаются в зависимости от проектных требований к бетону: компенсация усадки, достижение требуемых величин линейного расширения и самонапряжения и т. п. Каждый индивидуальный случай применения такого рода добавок в бетоне требует дополнительных исследований в бетоне по действующим ТНПа, которые занимают от 14 до 28 сут. В ряде случаев такой период испытаний является слишком длительным, и требуются ускоренные методы определения эффективности. В данной статье представлены исследования возможности применения в качестве одного из критериев эффективности расширяющейся добавки пуццолановой активности. Обоснована возможность определения пуццолановой активности по ускоренной методике Чапеля, что позволит в короткий период времени (1-2 сут) определиться с выбором той либо иной расширяющейся добавки. В качестве исследуемых добавок рассмотрены расширяющиеся комплексы на основе механических смесей глиноземистого цемента и гипса, метакаолина и гипса, также с добавлением извести. Предложен диапазон необходимых для получения цементов с компенсированной усадкой или самонапряжением 1 МПа значений пуццолановой активности. The use of expansive additives based on sulpho-alumina compositions to modify cement systems not only compensates for shrinkage, but in some cases allows for expansion and self-stressing. Today the market is replete with expansive additives based on sulfoaluminate compositions, which are both artificially synthesized materials and mechanical mixtures based on metakaolin, high alumina cement and gypsum (type “M” cement). The choice of a particular type of additive, as well as its dosage, is determined depending on the design requirements for concrete: shrinkage compensation, achieving the required values of linear expansion and self-stress, etc. Each individual case of this type of concrete admixture requires additional research in concrete under the existing norms, which take 14 to 28 days. In some cases, such a test period is too long and requires accelerated methods to determine efficiency. This article presents research into the possibility of using the pozzolana activity of expansive additive as one of the performance criteria. It has been substantiated that pozzolanic activity can be determined using the accelerated Chapelle test, which will allow a short period of time (1-2 days) to determine the choice of a particular expansive additive. Expansive complexes based on mechanical mixtures of alumina cement and gypsum, metakaolin and gypsum, also with the addition of lime, have been considered as additions under study. The range of pozzolanic activity values required to produce cements with compensated shrinkage or self-stress of 1 MPa is proposed.

Experimental Study on the Shrinkage Behavior and Mechanical Properties of AAM Mortar Mixed with CSA Expansive Additive

In this study, a calcium sulfoaluminate-based expansive additive (0%, 2.5%, 5.0%, and 7.5% by the mass of the binder) was added to compensate for the shrinkage of alkali-activated material (AAM) mortar. Modulus of elasticity curves based on the ACI 209 model were derived for the AAM mortar mixed with the additive by measuring the compressive strength and modulus of elasticity. Moreover, autogenous shrinkage and total shrinkage were measured for 150 days, and drying shrinkage was calculated by excluding autogenous shrinkage from total shrinkage. For the autogenous and drying shrinkage of AAM mortar, shrinkage curves by age were obtained by deriving material constants using the exponential function model. Finally, shrinkage stress was calculated using the modulus of elasticity of the AAM mortar and the curves obtained using the shrinkage model. The results showed that the calcium sulfoaluminate-based expansive additive had an excellent compensation effect on the drying shrinkage of AAM mortar, but the effect was observed only at early ages when the modulus of elasticity was low. From a long-term perspective, the shrinkage compensation effect was low when the modulus of elasticity was high, and thus, shrinkage stress could not be reduced.

Developing Large Slab Airport Runways for the Next Century

The purpose of this research was to determine whether shrinkage-compensating concrete (SCC) made with Type K cement can create durable airport runways with fewer joints and reduced maintenance costs. The primary criterion examined was the ability of SCC to offset the effects of early-age drying shrinkage when the concrete is acted upon by external restraint. The interaction of restraint with SCC is important because restraint resists the expansive behavior that provides shrinkage compensation. Four sets of experiments were conducted, with increasing levels of Type K expansive mineral additive in each set. A set of test specimens consisted of four-inch diameter restrained columns. Each set consisted of three columns with varying degrees of stiffness in the restraint frame, including low, medium, and high-restraint stiffness. The medium-restraint column provides the theoretical response of new pavement cast against a mature slab, whereas the other two bracket the problem. The column specimens were instrumented using vibrating wire strain gages, which were embedded in the concrete, and load cells, which were affixed to the top of the columns. This research concludes that SCC can be effective even with a stiff boundary condition, and that SCC provides the potential for much longer-lasting airport runway slabs, as a result of reduced shrinkage and therefore fewer cracks.