scholarly journals Accelerated and natural carbonation of concrete with high volumes of fly ash: chemical, mineralogical and microstructural effects

2019 ◽  
Vol 6 (1) ◽  
pp. 181665 ◽  
Author(s):  
Philip Van den Heede ◽  
Mieke De Schepper ◽  
Nele De Belie
Keyword(s):  
Fly Ash ◽  
High Volume ◽  
Test Results ◽  
X Ray Diffraction ◽  
Carbonation Reaction ◽  
High Volume Fly Ash ◽  
Carbonation Resistance ◽  
Microstructural Effects ◽  
Natural Carbonation ◽  
Mineralogical Phases

Today, a rather poor carbonation resistance is being reported for high-volume fly ash (HVFA) binder systems. This conclusion is usually drawn from accelerated carbonation experiments conducted at CO 2 levels that highly exceed the natural atmospheric CO 2 concentration of 0.03–0.04%. However, such accelerated test conditions may change the chemistry of the carbonation reaction (and the resulting amount of CH and C–S–H carbonation), the nature of the mineralogical phases formed (stable calcite versus metastable vaterite, aragonite) and the resulting porosity and pore size distribution of the microstructure after carbonation. In this paper, these phenomena were studied on HVFA and fly ash + silica fume (FA + SF) pastes after exposure to 0.03–0.04%, 1% and 10% CO 2 using thermogravimetric analysis, quantitative X-ray diffraction and mercury intrusion porosimetry. It was found that none of these techniques unambiguously revealed the reason for significantly underestimating carbonation rates at 1% CO 2 from colorimetric carbonation test results obtained after exposure to 10% CO 2 that were implemented in a conversion formula that solely accounts for the differences in CO 2 concentration. Possibly, excess water production due to carbonation at too high CO 2 levels with a pore blocking effect and a diminished solubility for CO 2 plays an important role in this.

Effect of Nano Silica and Ultrafine Fly Ash on Compressive Strength of High Volume Fly Ash Mortar

2013 ◽  
Vol 368-370 ◽  
pp. 1061-1065 ◽  
Author(s):  
Steve W.M. Supit ◽  
Faiz U.A. Shaikh ◽  
Prabir K. Sarker
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
High Volume ◽  
Partial Replacement ◽  
Strength Development ◽  
Test Results ◽  
X Ray Diffraction ◽  
Nano Silica ◽  
High Volume Fly Ash ◽  
Class F Fly Ash

This paper evaluates the effect of Ultrafine Fly Ash (UFFA) and nanoSilica (NS) on compressive strength of high volume fly ash (HVFA) mortar at 7 days and 28 days. Three series of mortar mixes are considered in the first part of this study. In the first series the effect of high content of class F fly ash as partial replacement of cement at 40, 50 and 60% (by wt.) are considered. While in the second and third series, the UFFA and NS are used as partial replacement of cement at 5%, 8%, 10%, 12% and 15% and 1%, 2%, 4%, 6% and 8% (by wt.) of cement, respectively. The UFFA and the NS content which exhibited highest compressive strength in the above series are used in the second part where their effects on the compressive strength of HVFA mortars are evaluated. Results show that the mortar containing 10% UFFA as partial replacement of cement exhibited the highest compressive strength at both 7 and 28 days among all UFFA contents. Similarly, the mortar containing 2% NS as partial replacement of cement exhibited the best performance. Interestingly, the use of UFFA in HVFA mortars did not improve the compressive strength. However, the use of 2% and 4% NS showed improvement in the compressive strength of HVFA mortar containing 40% and 50% fly ash at both ages. The effects of NS and UFFA on the hydration and strength development of HVFA mortar is also evaluated through X-Ray Diffraction (XRD) test. Results also show that the UFFA and NS can significantly reduce the calcium hydroxide (CH) in HVFA mortars.

Influence of Fly Ash on the Mechanical Properties of Engineered Cementitious Composites Cured at High Temperature

2010 ◽  
Vol 113-116 ◽  
pp. 1293-1296
Author(s):  
Yu Zhu ◽  
Ying Zi Yang ◽  
Hong Wei Deng ◽  
Yan Yao
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Fly Ash ◽  
High Volume ◽  
Bending Test ◽  
Cementitious Composites ◽  
Test Results ◽  
Four Point Bending ◽  
High Volume Fly Ash ◽  
Compressive Strength Test

In order to investigate the mechanical properties of cementitious composites (ECC) cured at 60°C, four-point bending test and compressive strength test are employed to analyze the effect of fly ash on the properties of ECC. The replacement ratio of cement with fly ash is 50%, 70% and 80%, respectively. The test results indicate that ECC with high volume fly ash still remain the characteristic of pseudo-strain hardening and the deflection of ECC increases remarkably by adding more fly ash. The observations of ECC indicate that the crack width is relatively smaller for higher volume fly ash ECC. Meanwhile, compressive strength of ECC specimens with 80% fly ash can reach to 70MPa. This is helpful to produce precast ECC with high volume of fly ash.

scholarly journals Experimental Research on Durability Properties of High Volume Fly Ash Concrete with Polypropylene Fibre

2019 ◽  
Vol 8 (6S4) ◽  
pp. 1039-1042
Keyword(s):  
Fly Ash ◽  
High Volume ◽  
Polypropylene Fibre ◽  
Test Results ◽  
Conventional Concrete ◽  
Fly Ash Concrete ◽  
High Volume Fly Ash ◽  
Chloride Resistance ◽  
Water Absorption Test ◽  
Strength And Durability

This study focuses on the influence of the durable properties of Conventional concrete and High volume fly ash concrete. Fly ash is replaced in various percentages as 0%,40%,50%,55% and 60% by the weight of ordinary Portland cement in addition to that polypropylene fibre of 0.2% is added for improving the strength and Durability of concrete. Water absorption test, chloride resistance test, sulphateresistance test and Rapid Chloride Penetration test (RCPT) were evaluated. The test results show that the addition of high volume fly ash and polypropylene fibre improves the flexural strength and Durability of concrete.Fly Ash replacement of 55% by the weight of cement is considered as the optimum replacement level

Effects of Compressive Strength and Carbonation of HCSA Amount on High Volume Fly Ash Concrete

2011 ◽  
Vol 261-263 ◽  
pp. 333-337
Author(s):  
Juan Hong Liu ◽  
Fang Fang Hou ◽  
Shao Min Song ◽  
Bo Ya Jia
Keyword(s):  
Compressive Strength ◽  
Fly Ash ◽  
Internal Structure ◽  
High Volume ◽  
Carbonation Depth ◽  
Fly Ash Concrete ◽  
Resistance Increase ◽  
Expansive Concrete ◽  
High Volume Fly Ash ◽  
Carbonation Resistance

In this article, the effects of compressive strength and carbonation depth of HCSA mixing amount on high volume fly ash concrete have been investigated. Besides, the effects of compressive strength and carbonation depth of the fly ash amount on HCSA expansive concrete have been also analyzed. The results show that proper HCSA mixing amount can improve the compressive strength and anti-carbonation resistance. On the condition of 55% mixing amount of fly ash and 6% HCSA, the compressive strength for 28 days enhanced 8MPa, the carbonation depth decreased by 0.7mm, at the age of 70, the strength increased by 12MPa and the depth reduced 1.7mm; when the mixing amount of HCSA reaches 10%, the internal structure of concrete would be destroyed; In the case of 6% HCSA amount, the compressive strength and anti-carbonation resistance decreases with the increase of fly ash mixing amount. While comparing to the concrete without HCSA, the compressive strength and anti-carbonation resistance increase obviously.

scholarly journals Effects of Accelerated Carbonation Testing and by-Product Allocation on the CO2-Sequestration-to-Emission Ratios of Fly Ash-Based Binder Systems

2021 ◽  
Vol 11 (6) ◽  
pp. 2781
Author(s):  
Philip Van den Heede ◽  
Nele De Belie
Keyword(s):  
Fly Ash ◽  
Co2 Emissions ◽  
Co2 Sequestration ◽  
High Volume ◽  
Electricity Production ◽  
Cement Clinker ◽  
Economic Allocation ◽  
High Volume Fly Ash ◽  
Sequestration Potential ◽  
Natural Carbonation

Carbonation of cementitious binders implies gradual capture of CO2 and significant compensation for the abundant cement-related CO2 emissions. Therefore, one should always look at the CO2-sequestration-to-emission ratio (CO2SP/EM). Here, this was done for High-Volume Fly Ash (HVFA) mortar (versus two commercial cement mortars). Regarding their CO2 sequestration potential, effects of accelerated testing (at 1–10% CO2) on as such estimated natural carbonation degrees and rates were studied. Production related CO2 emissions were evaluated using life cycle assessment with no/economic allocation for fly ash. Natural carbonation rates estimated from accelerated tests significantly underestimate actual natural carbonation rates (with 29–59% for HVFA mortar) while corresponding carbonation degrees are significantly overestimated (67–74% as opposed to the actual 58% for HVFA mortar). It is advised to stick with the more time-consuming natural tests. Even then, CO2SP/EM values can vary considerably depending on whether economic allocation coefficients (Ce) were considered. This approach imposes significant portions of the CO2 emissions of coal-fired electricity production onto fly ash originating from Germany, China, UK, US and Canada. Ce values of ≥0.50% lower the potential CO2SP/EM values up to a point that it seems no longer environmentally worthwhile to aim at high-volume replacement of Portland cement/clinker by fly ash.

The Influence of Size Effect on High-Volume Fly-Ash Concrete’s Carbonation Resistance Performance

2011 ◽  
Vol 368-373 ◽  
pp. 1121-1124
Author(s):  
Li Fang Liu ◽  
Xiao Xia Niu ◽  
Wang Yu ◽  
Xiao Man Liu
Keyword(s):  
Blast Furnace ◽  
Fly Ash ◽  
Size Effect ◽  
Blast Furnace Slag ◽  
High Volume ◽  
Carbonation Depth ◽  
Granulated Blast Furnace Slag ◽  
High Volume Fly Ash ◽  
Carbonation Resistance ◽  
Furnace Slag

using fixed concrete slump method,the carbonation resistance of concretes with high-volume fly-ash and ground granulated blast-furnace slag had been studied, and make an approach to size- effect .The results show that the more fly-ash joined in,the more carbonation depth is deeper . The carbonation resistance of concretes with high-volume fly-ash and ggbs is better than only with high-volume fly-ash’s. Size effect on carbonation depth of concretes is also important . Carbonation depth will become deeper as soon as the block size improving .and the early improvement is bigger than the late .The more concretes with high-volume fly-ash and ground granulated blast-furnace slag,the size-effect on carbonation depth of concretes will be more evident.

The Study on Workability and Mechanical Properties of High Volume Fly Ash Underwater Concrete

2014 ◽  
Vol 905 ◽  
pp. 235-238
Author(s):  
Xu Zhang ◽  
Qiao Ling Liu ◽  
Yu Qing Hu
Keyword(s):  
Fly Ash ◽  
High Performance ◽  
Fresh Concrete ◽  
High Volume ◽  
High Volume Fly Ash ◽  
Carbonation Resistance ◽  
Mineral Mixture ◽  
Underwater Concrete ◽  
Flocculating Agent ◽  
Early Strength

In this paper, in order to resolve contradiction that is between high workability and anti-segregation in fresh concrete, low early strength and poor carbonation resistance property of concrete and high volume fly ash addition, high performance water reducer is used to reduce yield stress in fresh concrete, mineral mixture and flocculating agent are used to adjust viscosity and measure of activation enhances early strength of this concrete.

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