Study on the Increase of the Supporting Capacity of a Cement Milk Pile with Expansive Additives

In this study, an engineering characteristic test was conducted on cement milk using expansive additives during the construction of bored piles. Expansive additive mixtures with various mixing ratios were prepared according to the construction standards of the Korea Expressway Corporation. Segregation resistance, compressive strength, frictional resistance stress, scanning electron microscope images, porosity, and economic feasibility were analyzed. It was found that segregation effects due to expansive additive incorporation were insignificant, and it was confirmed that all specimens exceeded 0.5 N/mm2, the compressive strength standard of the Korea Expressway Corporation pile bearing capacity. Given a water–binder ratio of 83% mixed with 10% expansive additives, frictional resistance increased up to ~35%, skin friction force was significantly improved, and a cost-saving effect of up to ~33.24% was achieved.

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.

A Study on Initial Setting and Modulus of Elasticity of AAM Mortar Mixed with CSA Expansive Additive Using Ultrasonic Pulse Velocity

This study investigated the hardening process of alkali-activated material (AAM) mortar using calcium sulfoalumiante (CSA) expansive additive (CSA EA), which accelerates the initial reactivity of AAMs, and subsequent changes in ultrasonic pulse velocity (UPV). After the AAM mortar was mixed with three different contents of CSA EA, the setting and modulus of elasticity of the mortar at one day of age, which represent curing steps, were measured. In addition, UPV was used to analyze each curing step. The initial and final setting times of the AAM mortar could be predicted by analyzing the UPV results measured for 14 h. In addition, the dynamic modulus of elasticity calculated using the UPV results for 24 h showed a tendency similar to that of the static modulus of elasticity. The test results showed that the use of CSA EA accelerated the setting of the AAM mortar and increased the modulus of elasticity, and these results could be inferred using UPV. The proposed measurement method can be effective in evaluating the properties of a material that accelerates the initial reactivity.

Effect of Micro-MgO-based Expanding Agent on Rheological and UCS Properties of Well Cement at Early Age

<p>Well integrity issue is a major concern not only in the Oil and Gas industry but in the geo-storage field. For CO<sub>2</sub> sequestration, in particular, poor quality cement jobs render wells to suffer from possible CO<sub>2</sub> and formation fluid migration issues. In some cases, this migration issue maybe caused by the micro-fracture or micro-channel created during the chemical shrinkage and bulk shrinkage processes. Using some expandable cement system to cope with this issue is a promising way to mitigate this issue. In this study, we are exploring the effect of a kind of micro-MgO based expanding material on some principal properties of CO<sub>2</sub> sequestration well cement.</p><p>In these experiments, a typical cement formulation including various additives was used. Our focus of this pilot study was to investigate the effect of expandable materials on some typical physical-mechanical properties of Portland cement with different concentrations such as 0%, 1.0%, 2.0%, 3% by weight of cement (BWOC). Meanwhile, the pure Class G Portland cement slurry was also investigated as the base experiment. By use of API standard (RP 10B) procedures, those physical-mechanical properties of the cement slurry and set cement have been studied which mainly cover such aspects as rheology, fluid-loss of the cement slurry and uniaxial compressive strength (UCS) through experimental measures.</p><p>The experimental results indicate that UCS decreases gradually with increasing concentrations of the expanding additive. The density, free fluid, and rheology of cement slurry show consistently with the variation of expanding additive concentration. In addition, the fluid loss will increase relative gradually with the increment of expansive additive concentration. By increasing the concentration of expansive additive from 0% (w/w) to 3% (w/w), cement slurry’s rheological properties consistently behaved as the main properties as plastic viscosity (PV), yield point (YP) and gel strength (GS) of 10-seconds and 10-minutes with values varied around 262.33 cP, 5.25 lb/100ft<sup>2</sup>, 6.33 lb/100ft<sup>2</sup>, and 15.26 lb/100ft<sup>2 </sup>respectively. However, the UCS value behaves contrary to the rheology properties, which gradually decreased from 63.33 MPa to 33.54 MPa with the concentration, increased from 0% to 3%. As the UCS test conducted under the curing conditions as 150 ℃, 3000psi and 24hrs, this gradual decrease of UCS maybe because of the delayed hydration characteristics of micro-MgO. Despite this decrease in USC is not positive to prevent any stressed-induced micro-channel, these results are still interesting for further corresponding study and will make the understanding of MgO based expansive additive’s effect on Portland cement matrix more completely. As per other research results and our future experimental study plan, the delayed expansion of micro-MgO hydration will compensate for the chemical and bulk shrinkage issue after enough curing.</p><p>According to the literature review, there are few publications reporting results on micro-MgO based expandable cement systems based on Class G cement.  Through this study, we are expecting to manifest a trend between the concentration of expanding additive and the cement slurry properties. This will provide the technical reference and guidance for further study and application of expanding cement systems in the industry.</p>