Stability of Air Content in Fresh Concretes with PCE-Based Superplasticizers

Abstract

Air contents of concrete are necessary for concrete durability in freeze-thaw exposure. According to the Finnish concrete code, the target value for air content varies between 4% and 5.5% for XF - exposure classes. Lately in Finland, some cases showed an elevation of air contents up to 15% in fresh air-entrained concrete at construction site and in drilled concrete samples. The objectives of this study were to investigate the stability of air entrainment by measuring the air content elevation 30 minutes and 60 minutes after concrete mixing and investigating the concrete sensitivity to segregation. Composition of concretes used in this study include 7 different combination of PCE based superplasticizer and air-entraining agent admixtures, cement content of 425 kg/m3, two consistency classes S3 with water to cement ration of 0.33 and F5 with water to cement ration of 0.38. One cement type was used for all concrete mixes. The concretes were mixed for 2 minutes and 5 minutes mixing times. The results show that the elevation of the air content of fresh concrete depends on the consistency of the concrete and on the used combination of superplasticizer and air-entraining agents. The higher consistency classes concretes have more risk of air elevation with some combinations of PCE-based superplasticizers and air-entraining agents. The results also indicate that short mixing time would not be enough to achieve total effectivity of some air-entraining agents, especially for higher consistency classes concrete.

Compressive strength of core specimens drilled from concrete test cylinders

“…Thus, it is important that the results of the core tests lead to the correct conclusions on the compressive strength and in some cases even on the conformity of concrete. Extensive attention was paid to assessing the compressive strength of concrete via drilled cores in the late 2010s, when excessively high air content and thus very low values of compressive strength were reported by air‐entrained concrete used in some Finnish bridge and deck structures 7 …”

Enhancing the Performance of Roller-Compacted Concrete Pavement by Synergetic Improvement of Packing Density, Lubrication, and Moisture State of Recycled Concrete Aggregate

“…This improvement could be attributed to better compaction facilitated by superplasticizers, thereby developing a denser aggregate structure for fine RCA mixtures (Figure 5 b ). Further, this might be linked to the homogeneous dispersion of cement paste and enhancement in the system fluidity as a result of the combined effects of the steric and electrostatic repulsion mechanism ( 55 , 56 ). Negatively charged ions (carboxylic group) adsorbed on positively charged cement grains result in electrostatic repulsion, whereas bulky side chains (long polymeric chains) of the absorbed polycarboxylate ether separate the cement grains apart ( 55 , 57 ), as shown in Figure 6.…”

“…Interestingly, fine RCA with the inclusion of superplasticizers could achieve similar compressive strength as that of the control mixture in both dry and SSD states and could alleviate the detrimental effect of AM (Figure 7 b ). The inclusion of superplasticizers increase the cohesiveness of the concrete mixture owing to the homogeneous dispersion of cement particles, ease the compaction and lower the voids, and result in denser concrete mixtures ( 56 , 60 ). As a result of this, extra water needed to satisfy the water absorption of RCA could be mitigated, and better workability can be achieved ( 60 ).…”

Advancement in Sustainable 3D Concrete Printing: A Review on Materials, Challenges, and Current Progress in Australia

“…The initial objective was to reduce the water content in concrete that leads to decreased porosity, which results in reduced shrinkage, enhanced durability, and workability. Lignosulfonate compounds-based plasticizers came to the market as the first generation, which lowered the water-to-binder ratio to between 5% and 10% [83,84]. However, modern plasticizers can reduce the water content in concrete by up to 15%, while superplasticizers allow a reduction in water content by 30% or more.…”