Factors Influencing the Hydration, Dimensional Stability, and Strength Development of the OPC-CSA-Anhydrite Ternary System

Due to the advantages of high early strength and rapid setting, ternary systems consisting of ordinary Portland clinker (OPC), calcium sulphoaluminate (CSA) clinker, and anhydrite have broad application prospects. However, further studies need to be undertaken to find a more optimal mixing proportion of this ternary binder in order to meet basic performance requirements. In this paper, isothermal calorimetric tests, chemical shrinkage tests, drying shrinkage tests, and compressive strength tests were carried out to systematically identify the effect of the OPC/CSA ratio and anhydrite dosage on the hydration, mechanical property development, and dimensional stability of ternary binders. It was found that a higher CSA content leads to a higher cumulative hydration heat, a shorter acceleration period, and a delayed induction period, which can be ascribed to the retardation of C3S at a high aluminate concentration. However, a higher addition of anhydrite can retard the main peak of hydration despite promoting the intermediate peak and improving the hydration reaction rate. The drying shrinkage of blends decreases first along with the CSA proportion and then increases. Moreover, a higher anhydrite content mitigates the drying shrinkage and hinders the strength development. Finally, considering the properties of both the fresh and hardened binder, the ternary blends with 5% anhydrite and OPC/CSA ratios ranging from 3/7 to 2/8 were identified as most suitable for applications that require a high early strength, stable late strength, and small level of shrinkage.

The Apparent Activation Energy of a Novel Low-Calcium Silicate Hydraulic Binder

In this work, the apparent activation energy (Ea) of a novel low-calcium binder was, for the first time, experimentally determined, using a calorimetric approach. Additionally, a correlation between the Ea, measured at the acceleration period with the C/S ratio of the hydration product is proposed. The Ea of the prepared pastes was determined through isothermal calorimetry tests by calculating the specific rate of reaction at different temperatures, using two different approaches. When comparing the Ea, at the acceleration period of this novel binder with the one published for alite and belite, we observed that its value is higher, which may be a result of a different hydration product formed with a distinct C/S ratio. Finally, to study the temperature effect on the compressive strength at early ages, a set of experiments with mortars was performed. The results showed that the longer the curing time at 35 °C, the higher the compressive strength after 2 days of hydration, which suggests a higher initial development of hydration products. This study also indicated that the novel binder has a higher sensitivity to temperature when compared with ordinary Portland cement (OPC).

How design thinking help us to select startups for the acceleration period?

Purpose To avoid wastage of resources of a startup accelerator, this paper aims to present a model for accelerator managers’ decision-making to enter startups into acceleration and initial capitalization using a fuzzy Delphi approach and an affinity diagram is one of the design thinking tools. Design/methodology/approach The high failure rate of startups has led to a waste of resources and a lot of capital. This failure rate is much higher in the early stages of startups and subsequently higher risk. This is where startup accelerators play a role in supporting startups and provide startups with the capital needed to accelerate. The point to note at this point is that choosing the team with the lowest success potential by the accelerators will eliminate their capital and energy. The purpose of this research is to avoid this wastage. Findings In this research, using the Fuzzy Delphi method and aggregation of opinions of 5 experts and managers of the acceleration field, additional criteria were eliminated and 35 criteria were considered as final criteria of the evaluation model. In the final stage, a 10-member committee of managers, specialists and faculty members was formed and the criteria were grouped using the affinity diagram method. Finally, the final model was presented considering the components of a business plan. Originality/value Using design thinking methods and a combination of that with a fuzzy and quantitative method is one of the contributions of this research. Also, making a model for selection startups in the acceleration stage of fundraising is another value of this research.

Adaptive control of movement deceleration during saccades

As you read this text, your eyes make saccades that guide your fovea from one word to the next. Accuracy of these movements require the brain to monitor and learn from visual errors. A current model suggests that learning is supported by two different adaptive processes, one fast (high error sensitivity, low retention), and the other slow (low error sensitivity, high retention). Here, we searched for signatures of these hypothesized processes and found that following experience of a visual error, there was an adaptive change in the motor commands of the subsequent saccade. Surprisingly, this adaptation was not uniformly expressed throughout the movement. Rather, after experience of a single error, the adaptive response in the subsequent trial was limited to the deceleration period. After repeated exposure to the same error, the acceleration period commands also adapted, and exhibited resistance to forgetting during set-breaks. In contrast, the deceleration period commands adapted more rapidly, but suffered from poor retention during these same breaks. State-space models suggested that acceleration and deceleration periods were supported by a shared adaptive state which re-aimed the saccade, as well as two separate processes which resembled a two-state model: one that learned slowly and contributed primarily via acceleration period commands, and another that learned rapidly but contributed primarily via deceleration period commands.

Kinematic changes in goal-directed movements in a fear-conditioning paradigm

In individuals with a musculoskeletal disorder, goal-directed reaching movements of the hand are distorted. Here, we investigated a pain-related fear-conditioning effect on motor control. Twenty healthy participants (11 women and 9 men, 21.7 ± 2.7 years) performed a hand-reaching movement task. In the acquisition phase, a painful electrocutaneous stimulus was applied on the reaching hand simultaneous with the completion of reaching. In the subsequent extinction phase, the task context was the same but the painful stimulus was omitted. We divided the kinematic data of the hand-reaching movements into acceleration and deceleration periods based on the movement-velocity characteristics, and the duration of each period indicated the degree of impairment in the feedforward and feedback motor controls. We assessed the wavelet coherence between electromyograms of the triceps and biceps brachii muscles. In the acquisition phase, the durations of painful movements were significantly longer in both the acceleration and deceleration periods. In the extinction phase, painful movements were longer only in the acceleration period and higher pain expectation and fear were maintained. Similarly, the wavelet coherence of muscles in both periods were decreased in both the acquisition and extinction phases. These results indicate that negative emotional modulations might explain the altered motor functions observed in pain patients.

941 Post-Operative Outcomes of Patients Undergoing Surgery During the Acceleration Period of COVID-19 Infection

Introduction There are concerns around the safety of performing surgery during COVID-19 outbreaks with few sources of robust evidence. Method We analysed 5020 consecutive patients who underwent surgery during the acceleration phase of COVID-19 at our hospital from 31st January to 13th April 2020. Data were also analysed for all patients who had a COVID-19 positive test result during the same study period. Results 156 patients (3%) developed COVID-19 symptoms after surgery; 28 patients (<1%) subsequently had a positive swab result. All-cause mortality was 44 patients (0.9%); 33 deaths (75%) were due to non COVID-19 diagnoses. There were no adverse COVID-19 related outcomes in any of the 648 patients who had cancer operations. Of 28 COVID-19 positive patients, 11 died (8 orthopaedic, 2 urology, 1 vascular surgery) of which 10 had an emergency admission; all were over 70 years of age. Recent surgery was not an independent prognostic factor for survival after COVID-19 infection. 12% of positive COVID-19 swabs were from long-stay patients. Conclusions Of 5020 operative patients, 0.2% died from COVID-19 and most complications were not related to the infection. With careful consideration, surgery can be provided safely during times of COVID-19 outbreaks with particular emphasis on avoiding in-hospital transmission.

SIMULATION OF PEAK GROUND ACCELERATION AND PSEUDO SPECTRAL ACCELERATION OF PALU EARTHQUAKE SEPTEMBER 28TH 2018

The devastating earthquake Mw 7.4 hit Palu City, Central Sulawesi on September 28th, 2018, at 17:02:44 WIB. A high tsunami followed it. More than 2000 people died as a result of the earthquake and tsunami disaster. The latest evidence shows that the earthquake was categorized as a rare super shear earthquake. The earthquake shaking that hit Palu City is relatively large. Acceleration data are not available at the study site due to the lack of instrumentation in the area. The Authors present a simulation of peak ground acceleration (PGA) and pseudo-spectral acceleration (PSA) due to the earthquake in three locations Tatura Mall, Roa-Roa Hotel, and Antapura Hospital. PGA describes the maximum acceleration on the ground, while pseudo-spectral acceleration describes the acceleration of earthquake shaking from buildings with various floor numbers. Simulation of PGA and PSA to the three sites used three different Ground Motion Prediction Equation (GMPE) functions, BSSA14, CB14, and CY14, with the weighting of each Next Generation Attenuation (NGA) GMPE functions. The results of PGA simulation is about 0.22-0.23 g and show that in the three study site, it is more vulnerable to spectral acceleration period T=0.3 s or building with three floors or about 1-15 floors. These correlate with the level of damage caused by earthquakes which is more impact to relatively higher buildings.

The Relationship between Cementitious Composition and Properties of Ultrahigh Strength Concrete

It is well known that supplementary cementitious materials (SCMs) have obvious effects on the properties of concrete. In order to understand the relationship between cementitious materials and properties of ultrahigh strength concrete (UHSC), the cementitious compositions of UHSC were designed by the simple-centroid design method. The effects of cementitious compositions on the properties of UHSC were investigated. It was found that the incorporation of silica fume (SF) improved the flowability and strength of UHSC, but it decreased the time of acceleration period, calcium hydroxide (CH) content, and porosity of UHSC at a certain content. The incorporation of fly ash (FA) increased the flowability, time of acceleration period, and porosity of UHSC, but it decreased the strength and CH content of UHSC. The relationships between cement, silica fume, and fly ash and the properties of UHSC were calculated based on the simple-centroid design method.

Recharge response and kinematics of an unusual earthflow in Liechtenstein

Understanding landslide behavior over medium and long timescales is crucial for predicting landslide hazard and constructing accurate landscape evolution models. The behavior of landslides in soil that undergo periodic displacements, termed earthflows or compound soil slides, is especially difficult to forecast at these timescales. This is because velocities can increase by orders of magnitude over annual to decadal timescales, due to processes such as changing recharge conditions, erosion of the landslide toe, and retrogression of the landslide head. In this paper, we provide a detailed analysis of the Schlucher landslide, an unusual earthflow that is perched above the village of Malbun, Liechtenstein. This landslide had been displacing by 10 to 20 cm/year until 2015, when displacements on the order of 2 m/year occurred from 2016 to 2018. These large displacements damaged landslide mitigation measures, caused numerous surface deformation features, and threatened the local population downstream of the earthflow. This landslide has an unusually long monitoring record, with accurate displacement and climatic data available since 1983. We analyze this nearly 40-year monitoring time series to estimate recharge from snowmelt and rainfall, and its correlation with displacement. We also analyze recently collected, high-resolution surface and subsurface data in order to understand landslide response to recharge, landslide kinematics through time, and catastrophic failure potential. We find that interannual displacements can be explained with variations in recharge; however, periodic surges with recurrence times of tens of years must be explained by other mechanisms. In particular, recharge into the landslide during the recent acceleration (2016 to 2018) was not anomalously high. Instead, we argue that loss of internal strength is responsible for this recent acceleration period, and that this mechanism should be considered when forecasting the surge potential for certain earthflows and soil slides.

Investigation on the Effect of Hydroxyapatite Nanorod on Cement Hydration and Strength Development

This work investigated the effect of hydroxyapatite (HA) nanorods on the strength development and hydration of cement. Undispersed HA nanorods (HA-UD) and dispersed HA nanorods (HA-DN) were prepared by atom-efficient neutralization. The strength of mortars modified by HA nanorods was tested, as well as their compatibility with supplementary cementitious material. The hydration of HA-modified cement pastes was characterized via in situ X-ray diffraction, isothermal calorimetry and scanning electron microscopy. As the results suggest, the undispersed HA-DN caused a considerable increase in superplasticizer demand to achieve the same level of flow. Both HA nanorods showed a significant accelerating effect on early hydration, with approximately 100% strength enhancement at 12 h at 2.0% dosage. The effect on early strength of the nanorods is retained in systems with up to 30% fly ash in the binder mass. According to the characterizations, the rate of the hydration reaction in the acceleration period was enhanced by HA nanorods, and C3S consumption was also increased. In all of the testing situations, HA-DN showed superior performance, likely due to improved spatial distribution of the hydroxyapatites. The results suggest that proper dispersion of the nanorods is necessary to optimize its performance.