Early age shrinkage and moisture loss of concrete

2004 ◽  
Author(s):  
N. Berke
Keyword(s):  
Moisture Loss ◽  
Early Age

scholarly journals Early-Age Cracking Analysis of a HVFA Concrete Structure Based on Thermo-Hygro-Mechanical Modeling Combined with XFEM

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Wei Cui ◽  
Yanjun Luo ◽  
Shuang Peng
Keyword(s):  
Heat Dissipation ◽  
High Volume ◽  
Moisture Loss ◽  
Early Age ◽  
Hydration Degree ◽  
Concrete Core ◽  
Hydration Rate ◽  
Mechanical Field ◽  
High Volume Fly Ash ◽  
Reduced Rate

Due to the low hydration rate of high-volume fly ash (HVFA) concrete at early age, the temperature gradient between the concrete core and surfaces could be effectively reduced. However, the low hydration rate results in a lack of hydration degree for early-age HVFA concrete. Thus, during curing, compared to the strength of ordinary Portland cement (OPC), a subsequent lower one of HVFA concrete leads to a more sensitive response to inner stresses induced by thermal and moisture loads. Based on ABAQUS, in this paper, user subroutines in the temperature and moisture fields were developed, with regard to the hydration degree, for simulation of the temperature and moisture influences on concrete. Additionally, the Double Power Law (DPL) model was used to depict early-age deformations of concrete in the mechanical field. Combined with the extended finite element method (XFEM), another subroutine for early-age cracking analysis in the mechanical field was then developed. Together with aforementioned subroutines, a thermo-hygro-mechanical model is derived. For evaluation of early-age cracking initiation and propagation of a pier composed of HVFA concrete, the model was implemented with XFEM. The obtained results show that (1) temperature and restraints are the main causes of cracking; (2) moisture loss affects surface cracks on structures at early age; and (3) although the temperature difference between the core and surfaces is not much obvious due to the reduced rate of heat dissipation from hydration, cracking of early-age HVFA concrete is still likely to happen for its low early strength. Thus, timely curing is critical to prevent early cracking.

Development of Test Methodology and Model for Evaluation of Curing Effectiveness in Concrete Pavement Construction

2003 ◽  
Vol 1861 (1) ◽  
pp. 17-25 ◽  
Author(s):  
Jin-Hoon Jeong ◽  
Dan G. Zollinger
Keyword(s):  
Relative Humidity ◽  
American Concrete Institute ◽  
Concrete Pavement ◽  
Moisture Loss ◽  
Early Age ◽  
Test Methodology ◽  
Curing Method ◽  
Pavement Construction ◽  
Rate Of Evaporation ◽  
Evaporation Models

Early-age moisture loss from the surface of a concrete pavement may induce undesirable effects that play a factor in long-term performance. Early-age detrimental behavior such as slab curling, warping, delamination, and even plastic shrinkage cracking are affected by the amount of evaporation and the effectiveness of the curing medium. The rate of evaporation is a key item in the monitoring of the quality of the curing. However, most approaches for this are largely empirical and are useful only under laboratory conditions. The effective curing thickness concept is introduced as a method to evaluate the effectiveness of a curing method. The surface relative humidity has the biggest influence on both the effective curing thickness and the rate of evaporation. Thus, prediction of the rate of evaporation of the water from concrete depends on the relative humidity of the surface and is important for evaluation of the curing method. Existing evaporation models, including the American Concrete Institute nomograph, were evaluated for their capabilities in predicting evaporation from curing concrete. Data from a series of laboratory experiments with a modified version of Penman’s evaporation model are also presented.

The Shikani HME: A New Tracheostomy Heat and Moisture Exchanger

2020 ◽  
Vol 63 (9) ◽  
pp. 2921-2929
Author(s):  
Alan H. Shikani ◽  
Elamin M. Elamin ◽  
Andrew C. Miller
Keyword(s):  
Ex Vivo ◽  
Moisture Loss ◽  
Speaking Valve ◽  
Time Zero ◽  
In Series ◽  
Turbulent Airflow ◽  
The Difference ◽  
Loss Efficiency ◽  
Heat And Moisture ◽  
Lung Simulation

Purpose Tracheostomy patients face many adversities including loss of phonation and essential airway functions including air filtering, warming, and humidification. Heat and moisture exchangers (HMEs) facilitate humidification and filtering of inspired air. The Shikani HME (S-HME) is a novel turbulent airflow HME that may be used in-line with the Shikani Speaking Valve (SSV), allowing for uniquely preserved phonation during humidification. The aims of this study were to (a) compare the airflow resistance ( R airflow ) and humidification efficiency of the S-HME and the Mallinckrodt Tracheolife II tracheostomy HME (M-HME) when dry (time zero) and wet (after 24 hr) and (b) determine if in-line application of the S-HME with a tracheostomy speaking valve significantly increases R airflow over a tracheostomy speaking valve alone (whether SSV or Passy Muir Valve [PMV]). Method A prospective observational ex vivo study was conducted using a pneumotachometer lung simulation unit to measure airflow ( Q ) amplitude and R airflow , as indicated by a pressure drop ( P Drop ) across the device (S-HME, M-HME, SSV + S-HME, and PMV). Additionally, P Drop was studied for the S-HME and M-HME when dry at time zero (T 0 ) and after 24 hr of moisture testing (T 24 ) at Q of 0.5, 1, and 1.5 L/s. Results R airflow was significantly less for the S-HME than M-HME (T 0 and T 24 ). R airflow of the SSV + S-HME in series did not significant increase R airflow over the SSV or PMV alone. Moisture loss efficiency trended toward greater efficiency for the S-HME; however, the difference was not statistically significant. Conclusions The turbulent flow S-HME provides heat and moisture exchange with similar or greater efficacy than the widely used laminar airflow M-HME, but with significantly lower resistance. The S-HME also allows the innovative advantage of in-line use with the SSV, hence allowing concurrent humidification and phonation during application, without having to manipulate either device.

A Community Based High Risk Register for Hearing Loss

1982 ◽  
Vol 47 (4) ◽  
pp. 373-375 ◽  
Author(s):  
James L. Fitch ◽  
Thomas F. Williams ◽  
Josephine E. Etienne
Keyword(s):  
Hearing Loss ◽  
System Identification ◽  
High Risk ◽  
Language Learning ◽  
Education Program ◽  
Communication System ◽  
Auditory Signal ◽  
Early Age ◽  
Community Based ◽  
Children With Hearing Loss

The critical need to identify children with hearing loss and provide treatment at the earliest possible age has become increasingly apparent in recent years (Northern & Downs, 1978). Reduction of the auditory signal during the critical language-learning period can severely limit the child's potential for developing a complete, effective communication system. Identification and treatment of children having handicapping conditions at an early age has gained impetus through the Handicapped Children's Early Education Program (HCEEP) projects funded by the Bureau of Education for the Handicapped (BEH).

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