THE USE OF POLYPROPYLENE FIBERS AGAINST PLASTIC SHRINKAGE CRACKING

2016 ◽  
Vol 3 (1) ◽  
Author(s):  
Hasan Nuri Turkmenoglu ◽  
Hakan Nuri Atahan ◽  
Cengiz Sengul
Keyword(s):  
Relative Humidity ◽  
Wind Velocity ◽  
Fresh Concrete ◽  
Polypropylene Fibers ◽  
Short Fibers ◽  
Shrinkage Cracking ◽  
Plastic Shrinkage ◽  
Concrete Temperature ◽  
Rate Of Evaporation

Plastic shrinkage cracking (PShC) occurs within a few hours after fresh concrete formed into the molds and it takes part on the surface of the concrete. When concrete formed into the molds, the aggregates settle because of the gravity and in contrast, water bleeds. If the rate of evaporation is higher than the rate of bleeding, surface of concrete starts to shrink. However, under the surface, the fresh concrete cannot shrink as much as the surface. Because of this condition, cracking occurs on the surface of concrete. In this respect, the quantity of PShC majorly depends on the temperature of concrete, temperature of air, rate of relative humidity and the wind velocity. Use of short fibers in concrete is one of the most effective ways to prevent concrete from PShC. The aim of this research was to evaluate the effect of polypropylene fibers having different geometries and content on PShC. For this purpose, the principles of ASTM C 1579 standard was considered. Results have shown that the use of polypropylene fibers in limiting PShC is obvious. Moreover, fibrillated fibers has shown better performance than monofilament fibers.

scholarly journals REUSED TYRE POLYMER FIBRE FOR FIRE-SPALLING MITIGATION

2016 ◽  
Author(s):  
Shan-Shan Huang ◽  
Harris Angelakopoulos ◽  
Kypros Pilakoutas ◽  
Ian Burgess
Keyword(s):  
Fresh Concrete ◽  
High Strength ◽  
Plain Concrete ◽  
Superior Performance ◽  
Polymer Fibre ◽  
Explosive Spalling ◽  
Polypropylene Fibres ◽  
Shrinkage Cracking ◽  
Plastic Shrinkage ◽  
The Eu

<p>Polypropylene fibres (PPF) are used in concrete principally to reduce plastic shrinkage cracking, but also to prevent explosive spalling of concrete exposed to fire. In the EU alone, an estimated 75,000 tonnes of virgin PPF are used each year. At the same time an estimated 63,000 tonnes of polymer fibres are recovered from end-of-life tyres, which are agglomerated and too contaminated with rubber to find any alternative use; currently these are mainly disposed of by incineration. The authors have initiated a study on the feasibility of reusing tyre polymer fibres in fresh concrete to mitigate fire-induced spalling. If successful, this will permit replacement of the virgin PPF currently used with a reused product of equal or superior performance. A preliminary experimental investigation is presented in this paper. High-strength concrete cubes/slabs have been tested under thermo-mechanical loading. This study has shown promising results; the specimens with the tyre polymer fibres have shown lower vulnerability to spalling than those of plain concrete.</p>

Experimental Study on the Early Shrinkage-cracking Property of the Polypropylene Fibe Concrete

2011 ◽  
Vol 236-238 ◽  
pp. 2259-2263
Author(s):  
Xian Song Xie
Keyword(s):  
Experimental Study ◽  
Autogenous Shrinkage ◽  
Drying Shrinkage ◽  
Early Age ◽  
Polypropylene Fibers ◽  
Free Shrinkage ◽  
Shrinkage Cracking ◽  
Plastic Shrinkage ◽  
Hardening Process ◽  
The Impact

Early shrinkage of concrete includes plastic shrinkage before the final setting, drying shrinkage during hardening process and autogenous shrinkage. Concrete drying shrinkage which is caused by evaporation is a major factor for the concrete volume change. By ring constrained test and free shrinkage CONCEN test, this paper studies the impact of polypropylene fibers on the shrinkage properties of concrete at the early age. The test shows that the polypropylene fibers can significantly reduce the early shrinkage of concrete, the best content of C30 concrete should be 0.9kg/m3.

scholarly journals A practical approach for reducing the risk of plastic shrinkage cracking of concrete

2017 ◽  
Vol 2 ◽  
pp. 40-44 ◽  
Author(s):  
Sadegh Ghourchian ◽  
Mateusz Wyrzykowski ◽  
Pietro Lura
Keyword(s):  
Capillary Pressure ◽  
Conventional Method ◽  
Fresh Concrete ◽  
Practical Approach ◽  
Shrinkage Cracking ◽  
Bleeding Rate ◽  
Conservative Method ◽  
Plastic Shrinkage ◽  
The Times

In this letter, a conventional method for mitigation of plastic shrinkage of fresh concrete based on comparing bleeding and evaporation rates (the former based on the commonly observed values of bleeding rate and the latter estimated by means of the commonly-used ACI nomograph) is critically assessed. It is shown that even if the initial bleeding rates are sufficiently high (i.e. higher than the evaporation rates), cracking may still occur if all the bleed water is lost by evaporation between the times of initial and final set, leading to the rise of capillary pressure. An alternative and more conservative method should be thus based on the total (accumulated) amount of bleed water compared to the total amount of evaporated water. The former should take into account the concrete’s properties and the geometry of the member, while the latter can be assumed based on the nomograph method.

Typical plastic shrinkage cracking behaviour of concrete

2013 ◽  
Vol 65 (8) ◽  
pp. 486-493 ◽  
Author(s):  
Riaan Combrinck ◽  
William Peter Boshoff
Keyword(s):  
Shrinkage Cracking ◽  
Plastic Shrinkage

scholarly journals Associations of Ambient Air Pollutants and Meteorological Factors With COVID-19 Transmission in 31 Chinese Provinces: A Time Series Study

2021 ◽  
Vol 58 ◽  
pp. 004695802110602
Author(s):  
Han Cao ◽  
Bingxiao Li ◽  
Tianlun Gu ◽  
Xiaohui Liu ◽  
Kai Meng ◽  
...  
Keyword(s):  
Air Pollution ◽  
Relative Humidity ◽  
Wind Velocity ◽  
Air Pollutants ◽  
Meteorological Factors ◽  
Meta Analysis ◽  
Ambient Air ◽  
Air Pollutant ◽  
Pollutant Concentrations ◽  
Air Pollutant Concentrations

Evidence regarding the effects of environmental factors on COVID-19 transmission is mixed. We aimed to explore the associations of air pollutants and meteorological factors with COVID-19 confirmed cases during the outbreak period throughout China. The number of COVID-19 confirmed cases, air pollutant concentrations, and meteorological factors in China from January 25 to February 29, 2020, (36 days) were extracted from authoritative electronic databases. The associations were estimated for a single-day lag as well as moving averages lag using generalized additive mixed models. Region-specific analyses and meta-analysis were conducted in 5 selected regions from the north to south of China with diverse air pollution levels and weather conditions and sufficient sample size. Nonlinear concentration–response analyses were performed. An increase of each interquartile range in PM2.5, PM10, SO2, NO2, O3, and CO at lag4 corresponded to 1.40 (1.37–1.43), 1.35 (1.32–1.37), 1.01 (1.00–1.02), 1.08 (1.07–1.10), 1.28 (1.27–1.29), and 1.26 (1.24–1.28) ORs of daily new cases, respectively. For 1°C, 1%, and 1 m/s increase in temperature, relative humidity, and wind velocity, the ORs were 0.97 (0.97–0.98), 0.96 (0.96–0.97), and 0.94 (0.92–0.95), respectively. The estimates of PM2.5, PM10, NO2, and all meteorological factors remained significantly after meta-analysis for the five selected regions. The concentration–response relationships showed that higher concentrations of air pollutants and lower meteorological factors were associated with daily new cases increasing. Higher air pollutant concentrations and lower temperature, relative humidity and wind velocity may favor COVID-19 transmission. Controlling ambient air pollution, especially for PM2.5, PM10, NO2, may be an important component of reducing risk of COVID-19 infection. In addition, as winter months are arriving in China, the meteorological factors may play a negative role in prevention. Therefore, it is significant to implement the public health control measures persistently in case another possible pandemic.

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