scholarly journals Study on the Heat of Hydration and Strength Development of Cast-In-Situ Foamed Concrete

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Wenhui Zhao ◽  
Qian Su ◽  
Feng Han ◽  
Wubin Wang
Keyword(s):  
Fly Ash ◽  
Ash Content ◽  
Heat Of Hydration ◽  
Maximum Temperature ◽  
Strength Development ◽  
Maximum Temperature Difference ◽  
Curing Conditions ◽  
Temperature Change Rate ◽  
Foamed Concrete

This study aims to investigate the relationship between the heat of hydration and the strength development of cast-in-situ foamed concrete. First, indoor model tests are conducted to determine the effects of the casting density and the fly ash content on the hydration heat of foamed concrete in semiadiabatic conditions. Second, compression tests are carried out to evaluate the development of the compressive strength with the curing time under standard curing conditions and temperature matched curing conditions. Third, the hydration heat development of the foamed concrete is tested in four projects. The results showed that the peak temperature, the maximum temperature change rate, and the maximum temperature difference increased with the increase in the casting density at different positions in the foamed concrete. For the same casting density of the foamed concrete, the peak temperature, the maximum temperature change rate, and the maximum temperature difference decreased with the increase in the fly ash content. For the foamed concrete without the admixture, the early strength was significantly higher under temperature matched curing conditions than under standard curing conditions, but the temperature matched curing conditions had a clear inhibitory effect on the strength of the foamed concrete. The strengths during the early stage and the later stage were both improved under temperature matched curing conditions after adding the fly ash, and the greater the fly ash content, the larger the effect. The maximum temperature increments were higher in the indoor model test than in the field tests for the same casting density. Reasonable cooling measures and the addition of fly ash decreased the maximum temperature increments and increased the corresponding casting times.

scholarly journals Abrasion-Resistant and Temperature Control of Lining Concrete for Large-Sized Spillway Tunnels

2020 ◽  
Vol 10 (21) ◽  
pp. 7614
Author(s):  
Qiang Yao ◽  
Shunchao Qi ◽  
Faming Wu ◽  
Xingguo Yang ◽  
Hongtao Li
Keyword(s):  
Fly Ash ◽  
Short Duration ◽  
Temperature Control ◽  
Performance Test ◽  
Early Stage ◽  
High Flow ◽  
Maximum Temperature ◽  
Measured Temperature ◽  
Maximum Temperature Difference ◽  
Morphological Effect

With regard to the high anti-scouring and abrasion-resistant performance requirements and great temperature control difficulties of lining concrete for large-sized spillway tunnels, in this study, a performance test was conducted on anti-scouring and abrasion-resistant concrete. The finite element method was used to analyze the temperature change rules of sidewall C9050 (design strength of concrete is 50 MPa at 90 days) lining concrete for the spillway tunnel. Further, a new cooling measure was proposed for adopting “early-throughput, high-flow and short-duration”. As indicated by the results of this study, fly ash could reduce water consumption and micro-cracks via its “morphological effect”. Silica fume could improve the early strength of cement concrete and make up for the strength loss caused by fly ash. Polyvinyl alcohol (PVA) fiber could enhance concrete durability. The doping of these three additives reinforced the strength and abrasion resistance of concrete. The results showed that the temperature of the lining concrete presented a change trend of “rapid increase first, followed by a slow decrease”. The peak temperature was reached roughly 2 days after casting. In addition, properly increasing throughput flow or decreasing throughput temperature in the early stage of casting could significantly reduce the highest temperature and maximum temperature difference of concrete. Based on the results from the numerical simulation of temperature control effect, it was proposed to adopt “early-throughput, high-flow, and short-duration” for temperature control and cracking prevention. Specifically, within 2 days after casting, cooling water at roughly 12 °C was guided in at a flow of approximately 3.5 m3/h. Within 3–7 days after casting, river water at around 17 °C was guided in at a flow rate of approximately 1.8 m3/h. After 7 days, the cooling effect can be well achieved by only using the surface flowing water for curing. According to the field monitoring data, the changes in measured temperature were basically consistent with those from numerical simulations, and detection on the temperature of the sidewall lining concrete showed that a qualification rate of >91% was satisfactorily obtained by using the proposed approach.

Study on Early Cracking Resistance of PC Box Girder Bridge

2010 ◽  
Vol 163-167 ◽  
pp. 1786-1792
Author(s):  
Wei Chun Zhong ◽  
Xiao Yi Zhang ◽  
Hui Zhou ◽  
Chuang Sheng Zheng
Keyword(s):  
Hydration Heat ◽  
Maximum Temperature ◽  
Strength Development ◽  
Cracking Resistance ◽  
Construction Stage ◽  
Maximum Temperature Difference ◽  
Construction Technique ◽  
Box Girder ◽  
Mixture Ratio ◽  
Girder Bridges

Early cracks of box girder are widespread during the construction stage of PC box girder bridges. The cracking resistance of a prestressed concrete continuous beam bridge was conducted from the point of construction technique. Experimental study on hydration heat and mechanical properties of box girder concrete at early age were carried out. The results shown that the casting temperature of the concrete, the peak temperature and the maximum temperature difference between inside and outside of the hydration heat were very low, which were 15.7°C, 8°C and 10.2°C, respectively. The strength development of the concrete was stable, and the mixture ratio was optimal. The concrete appearance quality was fairly good without visible cracks in the construction stage. The study reveals that the crack of girder bridges during the construction stage can be avoided by taking effective measures in the construction.

Early Age Property Study of Phosphate Cement by Electrical Conductivity Measurement

2013 ◽  
Vol 544 ◽  
pp. 409-414
Author(s):  
Zhu Ding ◽  
Xiao Dong Wang ◽  
Bi Qin Dong ◽  
Zong Jin Li ◽  
Feng Xing
Keyword(s):  
Electrical Conductivity ◽  
Fly Ash ◽  
Temperature Rise ◽  
Conductivity Measurement ◽  
Maximum Temperature ◽  
Strength Development ◽  
Initial Reaction ◽  
Early Age ◽  
Electrical Conductivity Measurement ◽  
Hardening Process

The properties and electrical conductivity at early age of magnesium phosphate cement (MPC) was studied. Electrical resistivity or conductivity had been used for explaining the microstructure development of cement materials. In the current study, an electrodeless resistivity meter (ERM) was used to study the early property of MPC, which was mixed with and without fly ash respectively. The hardening process was investigated by the conductivity variation, incorporating with strength development and temperature rise during the initial reaction. The products and microstructure morphology of MPC paste were analysed by XRD and SEM. Results showed the mechanical property of MPC can be improved by fly ash. Fly ash lowers the maximum temperature rise during initial reaction of MPC with water. The electrical conductivity results divids the hardening process of MPC into three stages: acceleration, deceleration and stabilization. Conductivity measurement is an excellent method to explain the hardening process of MPC.

Experimental Study on Carbonation Resistance of Ready-Mixed Concrete

2012 ◽  
Vol 174-177 ◽  
pp. 152-158 ◽  
Author(s):  
Jing Song Zhu ◽  
Ya Li Sun ◽  
Yue Feng Zhu ◽  
Dan Fei Chen
Keyword(s):  
Fly Ash ◽  
Service Life ◽  
Early Stage ◽  
Ash Content ◽  
Design Criteria ◽  
Carbonation Depth ◽  
Curing Conditions ◽  
Cement Ratio ◽  
Water Cement Ratio ◽  
Carbonation Resistance

By means of accelerated carbonation tests, the carbonation resistance of concrete in relation to the variation of water-cement ratio, fly ash content and curing conditions is studied in this article. The results show that under the standard curing conditions, with the fly ash content of 20%, in response to different water-cement ratio, the carbonation depth of concrete and the water-cement ratio are presented more or less in a linear relationship. At the water-cement ratio of 0.40, there is hardly any carbonation effect onto the concrete. However, at the ratio of bigger than 0.60, the carbonation depth of concrete increases in a speedy way. Under the standard curing conditions, at the water-cement ratio of 0.55, with the fly ash content of lower than or equal to 30%, the carbonation resistance of concrete is good enough to fulfill the design criteria of 50~100 years for service life of important and general buildings, while the compressive strength declines by less than 10%. But under the condition of 1d curing with retention of moisture followed by curing in the air until 28d, with no fly ash content, the carbonation depth of concrete has reached 35mm, which fails to fulfill the design criteria of 50 years for service life of general buildings. It is therefore concluded that the control of water-cement ratio, the control of fly ash content, and the sufficient curing with retention of moisture in early stage are all the essential factors to ensure the durability against carbonation for the concrete with fly ash content.

scholarly journals EFFECT OF FLY-ASH ON THE STRENGTH DEVELOPMENT OF COASTAL SOILS-A CASE STUDY FOR THE SOUTHERN COASTAL ZONE OF BANGLADESH

2021 ◽  
Vol 33 (1) ◽  
Author(s):  
O.C. Debanath ◽  
M.A Rahman ◽  
S. A. Chowdhury ◽  
R.U. Ahmed ◽  
S.N. Hassan ◽  
...  
Keyword(s):  
Fly Ash ◽  
Threshold Value ◽  
Ash Content ◽  
Performance Criteria ◽  
Strength Development ◽  
Deep Foundation ◽  
Environmental Threat ◽  
Residential Demand ◽  
Ground Stability

The rapid demand for urbanization expands the requirements of infrastructures and owing to the scarcity of available firm land; people are now built structures on soft soils. However, the application of a deep foundation for a low-rise structure may not be economically feasible for developing countries. The economic, as well as safe foundation, can be ensured by adopting traditional ground stability approaches. However, replacement of the industrial by-product, which possess minimum environmental threat may be a plausible option for ground stability. Therefore, an attempt is taken in this research to study the improvement of soft coastal soil by replacing with eco-friendly fly ash. The eastern bank of the river Karnaphuli, which has increasing industrial and residential demand is taken as a case study in this research. A series of experimental set-ups have been conducted to evaluate the strength development with different fly ash contents. It is found that the strength of fly ash treated soils increases with fly ash content up to a threshold value, and beyond that, the strength decreases. In addition, compaction and plasticity characteristics are also investigated through experimental observations and show better performance criteria with increasing fly ash contents. In a nutshell, this approach of replacing fly ash is suitable for coastal soil, and the experimental investigation reveals that an optimum 20% of fly ash content is justified.

scholarly journals Experiments on Foamed Concrete for the Development of Building Blocks

2020 ◽  
Vol 8 (5) ◽  
pp. 2824-2829
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Building Blocks ◽  
Ash Content ◽  
Partial Replacement ◽  
Dry Density ◽  
Load Bearing ◽  
Concrete Building ◽  
Concrete Blocks ◽  
Foamed Concrete

Foamed concrete is an innovative and versatile lightweight building material, which is a cement-based mortar consisting of at least 20% of its volume filled with air. Use of lightweight foamed concrete blocks with densities less than 1800 kg/m3 as infills will lead to the design of slender sections. Further, the thermal insulation properties of foamed concrete blocks made it more popular in construction industry. This paper discusses the development of foamed concrete building blocks for load bearing and non-load bearing structures. To make the mix more sustainable, the feasibility of fly ash as a partial replacement to cement is also explored. The variables considered for the production of foamed concrete are foam volume, water/powder (mix of cement and fly ash) ratio, fly ash content and sand/powder ratio. Analytical model is also developed for compressive strength and dry density of foamed concrete considering different variables and it is validated. Compressive strength is found to be increasing with the increase in dry density and with increase in fly ash content. Thermal conductivity is observed to be reduced by the addition of fly ash content

Study of Foamed Concrete from Activated Ash/Slag Blended Cement

2010 ◽  
Vol 160-162 ◽  
pp. 821-826 ◽  
Author(s):  
Feng Qing Zhao ◽  
Jun Qin Liu ◽  
Qian Li ◽  
Hao Li
Keyword(s):  
Thermal Conductivity ◽  
Fly Ash ◽  
Blended Cement ◽  
Drying Shrinkage ◽  
Curing Process ◽  
Low Carbon ◽  
Freezing And Thawing ◽  
Foaming Agent ◽  
Curing Conditions ◽  
Foamed Concrete

An ecotype of foamed concrete was prepared from activated fly ash/slag blended cement, a kind of low carbon cement, through physical foaming and hydrothermal curing process. The optimized material proportion and curing conditions were obtained with the aid of orthogonal array technique: activated fly ash/slag blended cement-600 kg and foaming agent-1kg for per cubic meter formed concrete, curing at 60°C for 6 hours. The density and compressive strength of the foamed concrete prepared in this method were 644kg/m3 and 4.5MP respectively, and with lower drying shrinkage and thermal conductivity, good freezing and thawing characteristics.

scholarly journals Study on Rheological and Mechanical Properties of Aeolian Sand-Fly Ash-Based Filling Slurry

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1266
Author(s):  
Xiaoping Shao ◽  
Long Wang ◽  
Xin Li ◽  
Zhiyu Fang ◽  
Bingchao Zhao ◽  
...  
Keyword(s):  
Fly Ash ◽  
Rheological Properties ◽  
Economic Benefits ◽  
Ash Content ◽  
Sand Fly ◽  
Strength Development ◽  
Hydration Reaction ◽  
Aeolian Sand ◽  
Delayed Reaction ◽  
Uniaxial Test

Backfill mining is the most environmentally friendly mining method at present, which can effectively control the surface subsidence, improve the recovery rate, and has good social and economic benefits. The purpose of this study is to solve the environmental problems caused by solid waste, combined with the rich geographical advantages of aeolian sand in the Yushenfu mining area of China. The rheological properties of the aeolian sand-fly ash-based filling slurry with different fly ash content are studied by experiments, and the strength development law of the filling body under different age and fly ash content are studied from the macroscopic and microscopic points of view. The rheological experiments showed that the increase of the amount of fly ash has a significant effect on the thixotropy, plastic viscosity, and yield stress of the filling slurry. Additionally, rheological properties of aeolian sand-fly ash-based filling slurry conform to the Bingham model. With the increase of the amount of fly ash, the performance of the filling slurry has been significantly improved. Uniaxial test and scanning electron microscope observation showed that the influence of fly ash on the strength of the filling body was mainly reflected in the late stage of maintenance, but was not obvious in the middle stage. Fly ash particles mainly bear the role of “water reduction” and a physical filling effect, which makes the filling slurry thicker and the internal structure more closely spaced. The volcanic ash reaction of fly ash is lagging behind the hydration reaction of cement; the secondary product of the delayed reaction is filled in the pores of cement hydrates, which can greatly reduce the porosity of the backfill body and increase the later strength of the backfill body. It provides a guarantee for the safe replacement of coal pillars in the working face.

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