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International Concrete Abstracts Portal

Showing 1-5 of 1494 Abstracts search results

Document: 

SP-349_13

Date: 

April 22, 2021

Author(s):

Gonzalo A. Lozano Rengifo, Mayra T. de Grazia, Leandro F. M. Sanchez, and Edward G. Sherwood

Publication:

Symposium Papers

Volume:

349

Abstract:

Reducing Normal Portland Cement (NPC) has been a major concern of concrete industry and research community over the last 2-3 decades. As much as 8% of the global CO2 emissions stem from clinker production. Hence, a wide number of research projects have been focusing on reducing NPC in cementitious materials using numerous strategies such as the use of supplementary cementing materials (SMC’s), limestone fillers (LF) and/or advanced mixproportioning techniques. Yet, the impact of these procedures on the overall behaviour of materials with low NPC content, especially in the fresh state and long-term durability, is still not fully understood. This work aims to understand the influence of the distance between the fine particles, the so-called Inter-Particle Separation (IPS), on the fresh state behaviour of cement-base pastes designed through the use of Particle Packing Models and incorporating LF. Evaluations on the fresh (i.e. rheological behaviour and setting time) and hardened states (compressive strength) were conducted in all mixtures. Results show that IPS directly correlates with the viscosity of cementbase pastes for all shear rates appraised. Moreover, the use of LF increases the hydration rate of NPC pastes. Finally, it is clear that the water-to-cement ratio keeps being the main factor controlling the compressive strength of cement pastes with reduced NPC content and high levels of LF replacement.


Document: 

SP-349_39

Date: 

April 22, 2021

Author(s):

Luigi Coppola, Denny Coffetti, Elena Crotti and Gabriele Gazzaniga

Publication:

Symposium Papers

Volume:

349

Abstract:

This paper presents an experimental study carried out to investigate the durability of one-part alkaliactivated slag (AAS) mortars in different aggressive environments, such as chloride- and sulphate-rich solutions or in presence of freezing-thawing cycles. The mixtures were manufactured at equal water content and were activated by using sodium silicate, potassium hydroxide and sodium carbonate in powder form. In particular, the behavior of AAS mortars with different alkali content was compared with that of mixtures based on Portland cement and blast-furnace cement. Results show that the alkali content is a key-parameter for the durability of these innovative binders. In fact, in mortars manufactured with an alkali content higher than 0.06 by binder mass, the strength loss is similar to those of mixtures based on blast furnace cement after 150 freeze/thaw cycles. On the contrary, the sulphate-rich solution promotes a stronger degradation of the slag-based mortars respect to that shown by cement-based mixtures, regardless of the alkali content. Finally, the strong deterioration of cement matrix promoted by the formation of oxychloride in CaCl2-rich environment is negligible in AAS mortars due to the lack of calcium hydroxide in the slag matrix.


Document: 

SP-349_49

Date: 

April 22, 2021

Author(s):

R.Douglas Hooton

Publication:

Symposium Papers

Volume:

349

Abstract:

Approximately 90% of the carbon footprint from concrete production is from portland cement (assuming portland cement is used as the sole cementitious binder). Therefore to reduce its carbon footprint, the amount of Portland cement clinker needs to be reduced. There are different ways of doing this, including optimization of combined aggregate gradations, use of water reducing admixtures, use of portland-limestone cements (PLC), and use of supplementary cementitious materials (SCMs). All of these measures can be taken simultaneously, but there is also concern that extreme measures (such as high SCM replacement levels) will reduce the robustness of concrete to abuse during construction, resulting in lower durability. Durability is important to obtain long service lives of concrete structures, and has a large impact on their carbon footprint.

This paper includes discussion of how each these measures if used prudently, can achieve significant reductions in carbon footprint while simultaneously improving durability in aggressive exposure conditions.


Document: 

SP-349_41

Date: 

April 22, 2021

Author(s):

Renan P. Salvador, Dimas A. S. Rambo, Roberto M. Bueno, Kaio T. Silva, and Antonio D. de Figueiredo

Publication:

Symposium Papers

Volume:

349

Abstract:

The use of additions to replace cement in sprayed concrete applications is crucial in order to obtain matrices with proper mechanical properties and durability. Blast-furnace slag is not commonly employed to produce sprayed concrete because of its low reactivity. In this context, the objective of this study is to evaluate the chemical and mechanical properties of sprayed concrete produced with cement and blast-furnace slag as a partial cement replacement. Hydration kinetics were characterized by isothermal calorimetry, while mechanical properties were evaluated by needle penetration resistance and compressive strength of extracted cores. Results showed that slag was activated by accelerators and the resulting matrix fulfilled the requirements of the strength class J 2 . Therefore, blast-furnace slag may be used in sprayed concrete when the average strength class is specified.


Document: 

SP-349_34

Date: 

April 22, 2021

Author(s):

Yuichi Yoshimura, Maki Mizuta, Hideyuki Sunaga, and Yoshie Otake

Publication:

Symposium Papers

Volume:

349

Abstract:

The development of a method to evaluate water penetration in concrete is beneficial for analyzing the durability of concrete structures since water in concrete affects the progress of degradations such as salt attack, carbonation, alkali silica reaction. However, water in concrete is generally detected by an embedded electric moisture sensor, it is difficult to obtain continuous spatial distribution about water diffusion. Water penetrated into concrete with a thickness of 5 cm was observed by neutron imaging using a room-size neutron source based on a compact accelerator and macroscopic analysis on water penetration was carried out. The results showed that the neutron transmittance corresponds to the water content and the moisture profile. Then transfer properties of water in concrete were obtained nondestructively and quantitatively. In addition, the relationship between the test results evaluating void structure and the water penetration resistance was considered. This report shows a new simple method to evaluate water penetration in concrete.


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