Preliminary Study on Reaction of Fresh Concrete with Carbon Dioxide

In order to let fresh concrete react with carbon dioxide sufficiently, the carbon dioxide was added to mixing concrete. The study used three water cement ratio (0.55, 0.65, 0.75), three CO2 pressures (0.2, 0.4, 0.6 MPa), and two CO2 concentration (50% and 100%) to make concrete samples, and observed the effect of carbon dioxide adsorption in the above parameters. Finally, the compressive strength and carbonation degree of concretes were tested after three curing time (7, 14 and 28 days). The research showed that concrete could be more efficient to absorb carbon dioxide by using this pressure method. The results found that the mixing concrete react with carbon dioxide in a short time, and shorten the initial setting time of concrete. But this method would greatly reduce the workability of concrete after mixing with carbon dioxide and it might be enhanced by water or superplasticizer. The bond of cement matrix might cut down after reacting with carbon dioxide. Based on the above, the compressive strength of concrete which was mixed with carbon dioxide would be impaired. The proposed CO2-mixing method has the capacity to uptake 9.5% carbon dioxide based on water cement ratio and CO2 pressure.

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Evaluation of initial setting time due to superplasticizers

Challenge Journal of Concrete Research Letters ◽

10.20528/cjcrl.2017.02.003 ◽

2017 ◽

Vol 8 (2) ◽

pp. 65

Author(s):

Abhishek Singh ◽

Shobha Ram ◽

Alok Verma

Keyword(s):

Water Content ◽

Cement Paste ◽

Setting Time ◽

Cement Ratio ◽

Water Cement Ratio ◽

Initial Setting Time ◽

Initial Setting

This paper shows how polycarboxylate based superplasticizer affects the initial setting time of cement paste. Three superplasticizers are used in this study with different properties and aiming to determine the delay in initial setting time due to superplasticizer. Initial setting time is calculated as per IS: 4031-PART 5-1988 with different SP dosages (0.5%, 0.75%, 1.0% and 1.5% of weight of cement). Superplasticizer is an admixture which reduces the water-cement ratio or increase the workability at the same water content. This paper deals with the evaluation of initial setting time due to superplasticizers.

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Experimental Study on Fluid Properties of Cement-Fly Ash Slurry Subjected to Multifactors

Geofluids ◽

10.1155/2021/9924895 ◽

2021 ◽

Vol 2021 ◽

pp. 1-17

Author(s):

Tian Huang ◽

Feng Huang ◽

Huifeng Zhou

Keyword(s):

Fly Ash ◽

Setting Time ◽

Factors Affecting ◽

Cement Ratio ◽

Water Cement Ratio ◽

Initial Setting Time ◽

Fluid Properties ◽

Practical Engineering ◽

Initial Setting ◽

The Stability

There are many factors affecting the characteristics of cement-fly ash slurry in practical engineering. Thus, this paper studies the influence of multifactors on the fluid properties of cement-fly ash slurry based on water-cement ratio ( w / c ) (0.75, 1, 1.25, and 1.5), fly ash content (0%, 10%, 20%, 30%, 40%, and 50%) and temperature (20°C, 40°C, 60°C, and 80°C). The bleeding ratio, initial setting time, final setting time, and viscosity were analyzed under coupling conditions. It is found that the water-cement ratio ( w / c ) is the main factor that affects the rheological properties and bleeding rate of slurry. The temperature affects the stability of the slurry in terms that the bleeding ratio of the slurry decreases as the temperature increases. The addition of fly ash enhances the stability of the slurry under different temperature conditions.

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Effect of Calcium Nitrate on the Properties of Portland–Limestone Cement-Based Concrete Cured at Low Temperature

Materials ◽

10.3390/ma14071611 ◽

2021 ◽

Vol 14 (7) ◽

pp. 1611

Author(s):

Gintautas Skripkiūnas ◽

Asta Kičaitė ◽

Harald Justnes ◽

Ina Pundienė

Keyword(s):

Compressive Strength ◽

Cement Paste ◽

Setting Time ◽

Calcium Nitrate ◽

Curing Temperature ◽

Hardened Concrete ◽

Cement Pastes ◽

Initial Setting Time ◽

Initial Setting ◽

Early Strength

The effect of calcium nitrate (CN) dosages from 0 to 3% (of cement mass) on the properties of fresh cement paste rheology and hardening processes and on the strength of hardened concrete with two types of limestone-blended composite cements (CEM II A-LL 42.5 R and 42.5 N) at different initial (two-day) curing temperatures (−10 °C to +20 °C) is presented. The rheology results showed that a CN dosage up to 1.5% works as a plasticizing admixture, while higher amounts demonstrate the effect of increasing viscosity. At higher CN content, the viscosity growth in normal early strength (N type) cement pastes is much slower than in high early strength (R type) cement pastes. For both cement-type pastes, shortening the initial and final setting times is more effective when using 3% at +5 °C and 0 °C. At these temperatures, the use of 3% CN reduces the initial setting time for high early strength paste by 7.4 and 5.4 times and for normal early strength cement paste by 3.5 and 3.4 times when compared to a CN-free cement paste. The most efficient use of CN is achieved at −5 °C for compressive strength enlargement; a 1% CN dosage ensures the compressive strength of samples at a −5 °C initial curing temperature, with high early strength cement exceeding 3.5 MPa but being less than the required 3.5 MPa in samples with normal early strength cement.

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Effect of Water Cement Ratios on Compressive Strength of Palm Kernel Shell Concrete

LAUTECH Journal of Civil and Environmental Studies ◽

10.36108/laujoces/9102/20(0121) ◽

2019 ◽

Vol 2 (Issue 1) ◽

Author(s):

A.O Adeyemi ◽

M.A Anifowose ◽

I.O Amototo ◽

S.A Adebara ◽

M.Y Olawuyi

Keyword(s):

Compressive Strength ◽

Coarse Aggregate ◽

Fresh Concrete ◽

Palm Kernel ◽

Hardened Concrete ◽

Cement Ratio ◽

Water Cement Ratio ◽

Palm Kernel Shell ◽

Compressive Strength Of Concrete ◽

Palm Kernel Shells

This study examined the effect of varying water cement ratio on the compressive strength of concrete produced using palm kernel shell (PKS) as coarse aggregate at different replacement levels. The replacement levels of coarse aggregate with palm kernel shells (PKS) were 0%, 25%, 50%, and 100% respectively. PKS concrete cubes (144 specimens) of sizes 150mm x 150mm x 150mm were cast and cured in water for 7, 14, 21 and 28 days respectively. A mix ratio of 1:2:4 was adopted with water-cement ratio of 0.45, 0.5, and 0.6 respectively while the batching was done by weight. Slump test was conducted on fresh concrete while compressive strength test was carried out on the hardened concrete cubes using a compression testing machine of 2000kN capacity. The result of tests on fresh concrete shows that the slump height of 0.45 water cement ratio (w/c) increases with an increase in PKS%. This trend was similar to 0.50 and 0.60 w/c. However, the compressive strength of concrete cube decreases with an increase in w/c (from 0.45 to 0.60) but increases with respect to curing age and also decreases with increase in PKS%. Concrete with 0.45 water-cement ratio possess the highest compressive strength. It was observed that PKS is not a good substitute for coarse aggregate in mix ratio 1:2:4 for concrete productions. Hence, the study suggest the use of chemical admixture such as superplasticizer or calcium chloride in order to improve the strength of palm kernel shells-concrete.

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Aplikasi Response Surface Methodology pada Optimasi Penambahan Blast Furnace Slag Terhadap Waktu Pengikatan dan Kuat Tekan Semen

Jurnal Teknik Kimia dan Lingkungan ◽

10.33795/jtkl.v4i1.150 ◽

2020 ◽

Vol 4 (1) ◽

pp. 61

Author(s):

Hardjono Hardjono ◽

Cucuk Evi Lusiani ◽

Agung Ari Wibowo ◽

Mochammad Agung Indra Iswara

Keyword(s):

Compressive Strength ◽

Response Surface Methodology ◽

Blast Furnace ◽

Response Surface ◽

Blast Furnace Slag ◽

Setting Time ◽

Initial Setting Time ◽

Initial Setting ◽

Central Composite ◽

Furnace Slag

Produksi semen setengah jadi (clinker) membutuhkan energi yang tinggi sehingga menggunakan batu bara dalam jumlah besar. Hal ini menyebabkan biaya produksi dari pabrik semen juga tinggi. Kebutuhan energi yang besar untuk menghasilkan clinker tersebut dapat dikurangi dengan menambahan blast furnace slag sebagai campuran pembuatan semen. Campuran clinker dapat menghasilkan produk semen yang memiliki waktu pengikatan dan kuat tekan sesuai SNI. Pengaruh penambahan blast furnace slag sebagai campuran clinker terhadap waktu pengikatan dan kuat tekan semen dapat dioptimalkan dengan response surface methodology (RSM) menggunakan Central Composite Design (CCD). Optimasi dengan menggunakan RSM bertujuan untuk mengetahui kondisi optimum pada penambahan blast furnace slag dan clinker terhadap variabel respon berupa waktu pengikatan awal, waktu pengikatan akhir, dan kuat tekan. Hasil uji ANOVA dan analisis response surface menunjukkan bahwa penambahan blast furnace slag sebagai campuran dalam pembuatan semen memberikan pengaruh yang signifikan terhadap waktu pengikatan awal, waktu pengikatan akhir, dan kuat tekan. Penambahan 5% blast furnace slag dengan 92,5% clinker pada campuran clinker dan gypsum merupakan kondisi optimum yang memberikan pengaruh signifikan terhadap variabel respon.The production of clinker consumes high energy and causes high production cost of cement industry. It can be reduced by adding blast furnace slag as a mixture in cement production. The blast furnace slag - clinker mixture can produce cement with setting time and compressive strength according to SNI. The effect of the addition of blast furnace slag as a clinker mixture to the setting time and compressive strength of cement can be optimized by response surface methodology (RSM) using Central Composite Design (CCD). Optimization by using RSM aims to determine the optimum condition of the blast furnace slag – clinker mixture to the initial setting time, final setting time, and compressive strength. ANOVA test results and response surface analysis show that the addition of blast furnace slag into the cement mixture has a significant influence on the initial setting time, final setting time, and compressive strength. The addition of 5% blast furnace slag with 92.5% clinker in the mixture of clinker and gypsum is the optimum condition which gives a significant effect on the response variable.

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Analysis of the Influence of Crystalline Admixtures at Early Age Performance of Cement-Based Mortar by Electrical Resistance Monitoring

Materials ◽

10.3390/ma14195705 ◽

2021 ◽

Vol 14 (19) ◽

pp. 5705

Author(s):

Rubén Beltrán Cobos ◽

Fabiano Tavares Pinto ◽

Mercedes Sánchez Moreno

Keyword(s):

Compressive Strength ◽

Thermogravimetric Analysis ◽

Remote Monitoring ◽

Electrical Resistance ◽

Setting Time ◽

Early Age ◽

Resistance Monitoring ◽

Initial Setting Time ◽

Characterization Techniques ◽

Initial Setting

Crystalline admixtures are employed for waterproofing concrete. This type of admixtures can affect the early age performance of cement-based mixes. The electrical resistance properties of cement have been related to the initial setting time and to the hydration development. This paper proposes a system for remote monitoring of the initial setting time and the first days of the hardening of cement-based mortars to evaluate the effect of the incorporation of crystalline admixtures. The electrical resistance results have been confirmed by other characterization techniques such as thermogravimetric analysis and compressive strength measurements. From the electrical resistance monitoring it has been observed that the incorporation of crystalline admixtures causes a delay in the initial setting time and hydration processes. The measurements also allow to evaluate the influence of the amount of admixture used; thus, being very useful as a tool to define the optimum admixture dosage to be used.

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Effect of retardant admixtures type and their using method on the behavior of concrete

Challenge Journal of Concrete Research Letters ◽

10.20528/cjcrl.2021.03.004 ◽

2021 ◽

Vol 12 (3) ◽

pp. 104

Author(s):

Tamer Ibrahim Ahmed ◽

Mohamed Roshdy Afify

Keyword(s):

Compressive Strength ◽

Fresh Concrete ◽

Setting Time ◽

Casting Process ◽

Additional Dose ◽

Construction Sites ◽

Effective Option ◽

Initial Setting ◽

Crisis Conditions ◽

Ready Mix Concrete

Construction sites may be exposed to crisis conditions during the casting process, resulting in delays of several hours and causing destruction of ready-mix concrete. This study suggests an experimental analysis of the possibility of using a specific additional dose of retardant admixtures, which may be used to ready-mix concrete before the initial setting of the concrete occurs. The effect of this additional dose on concrete characteristics in terms of workability, setting time, and compressive strength is also being studied. To conduct this investigation, three types of retardant admixtures from three branded companies were used. In addition, a penetration resistance experiment was conducted on the concrete to determine its setting time. The setting time of concrete was measured at different period intervals depending on when the additional dose of the retardant admixtures was added from the start of the concrete mixing. The results showed that concrete maintained proper workability for a period of more than 5 hours after using the additional dose of retarding admixtures. The additional dose of retarding admixtures not only delayed the concrete setting but also improved the compressive strength of the concrete. This implies that the use of an additional dose of retardant admixtures specifically tailored for ready-mix concrete is an effective option to avoid the return of ready-mixed fresh concrete.

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Influence of Water-Cement Ratio and Type of Mixing Water on the Early Hydration Performance of Calcium Sulphoaluminate (CSA) Cement

Advances in Materials Science and Engineering ◽

10.1155/2021/5557763 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Chuanlin Wang ◽

Meimei Song

Keyword(s):

Compressive Strength ◽

Physical Properties ◽

Setting Time ◽

Hydration Process ◽

Chemical Shrinkage ◽

Cement Ratio ◽

Water Cement Ratio ◽

Influence Of Water ◽

Calcium Sulphoaluminate ◽

Mixing Water

The present work studies the influence of water-cement ratio and types of mixing water on the hydration process and microstructure of calcium sulphoaluminate (CSA) cement. Experimental tests on the setting time, physical properties, compressive strength, chemical shrinkage, X-ray diffraction (XRD), and scanning electron microscopy (SEM) of CSA cement paste were carried out. The XRD analysis confirmed that the main hydration product is ettringite in both freshwater and seawater mixed CSA cement with different w/c ratios. The SEM analysis and physical properties test show that both low w/c ratio and seawater can improve the microstructure of CSA cement. The test results also find out that the high w/c ratio can accelerate the hydration process, extend the setting time, lower the compressive strength, and increase the chemical shrinkage of CSA cement, and the seawater presents a similar influence except for the mechanical property. The seawater increases the compressive strength of CSA cement in the early stage of hydration but will increase the microcracks at the later hydration stage of CSA cement and reduce its mechanical properties.

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Study of Calcium Acrylate on Compressive Strength and Hydration Process of Cement

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.816-817.161 ◽

2013 ◽

Vol 816-817 ◽

pp. 161-165

Author(s):

Fu Lan Wang ◽

Qi Wang ◽

Peng Song ◽

Zhong Xi Yang ◽

Lei Tian

Keyword(s):

Hydrogen Peroxide ◽

Compressive Strength ◽

Induction Period ◽

Setting Time ◽

Comprehensive Analysis ◽

Hydration Process ◽

Cross Linking ◽

Initial Setting Time ◽

Initial Setting ◽

Speed Up

In this paper, the hydration process and strength of calcium acrylate (CA) modified cement under the effects of different additives, such as, initiator-hydrogen peroxide, accelerator-triethanolamine, and cross-linking agent-butyl acrylate, were studied. Through comprehensive analysis, the optimal content of additives of initiator, cross-linking agent, and accelerator is ascertained 3%, 10% and 3%, respectively. On the condition of optimal content of additives and CA, it can be obtained that CA can increase the exothermic rate of cement within one hour and accelerate the exothermic rate in the induction period, shorten the time of the induction period, and speed up the initial setting time of cement. Besides, CA can inhibit the transformation of AFm from AFt, improve the dispersion of cement paste, make later hydration more fully, and promote later strength.

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Preparation and Performance of a New-Type Alkali-Free Liquid Accelerator for Shotcrete

Advances in Materials Science and Engineering ◽

10.1155/2017/1264590 ◽

2017 ◽

Vol 2017 ◽

pp. 1-9

Author(s):

Yanping Sheng ◽

Bin Xue ◽

Haibin Li ◽

Yunyan Qiao ◽

Huaxin Chen ◽

...

Keyword(s):

Compressive Strength ◽

Cement Paste ◽

Cement Mortar ◽

Retention Rate ◽

Setting Time ◽

Test Results ◽

Initial Setting Time ◽

Initial Setting ◽

New Type ◽

And Performance

A new type of alkali-free liquid accelerator for shotcrete was prepared. Specifically, the setting time and strength and shrinkage performance of two kinds of Portland cement with the accelerator were fully investigated. Moreover, the accelerating mechanism of alkali-free liquid accelerator and the hydration process of the shotcrete with accelerator were explored. Results show that alkali-free liquid accelerator significantly shortened the setting time of cement paste, where the initial setting time of cement paste with 8 wt% of the accelerator was about 3 min and the final setting time was about 7 min. Compressive strength at 1 day of cement mortar with the accelerator could reach 23.4 MPa, which increased by 36.2% compared to the strength of cement mortar without the accelerator, and the retention rate of 28-day compressive strength reached 110%. In addition, the accelerator still shows a good accelerating effect under low temperature conditions. However, the shrinkage rate of the concrete increased with the amount of the accelerator. 5~8% content of accelerator is recommended for shotcrete in practice. XRD and SEM test results showed that the alkali-free liquid accelerator promoted the formation of ettringite crystals due to the increase of Al3+ and SO42- concentration.

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