English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

K e y w o r d s : Anti-foaming admixture; Superplasticizer; Mortar; Concrete; Porosity; Workability; Compressive strength. 4/2019 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 61 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T The Si les ian Univers i ty of Technology No. 4/2019 d o i : 1 0 . 2 1 3 0 7 / A C E E 2 0 1 9 0 5 2 B . Ł a ź n i e w s k a P i e k a r c z y k average about 10%), so a strong mechanism of foam generation is common [1]. The sizes of pores formed during PCP action in hardened concrete are too big. The air content in the concrete mixture does not work only for its flow, but above all for final mechanical properties and durability of hardened concrete. There are four types of pores in concrete. Gel pores, the common size of (1.5–2.0) μm, have no negative effect on concrete strength due to porosity. However, they directly affect creep and shrinkage of concrete. Concrete strength is a function of the air volume. An increase in the percentage of macropores by 1% can reduce compressive strength by as much as 5%. It was found that pores with diameters smaller than 20 nm impose a negligible effect on compressive strength [3–6]. Nevertheless, it was claimed that pores from the range of 20–50 nm, rather than with diameters greater than 100 nm, have a greater influence on compressive strength [6]. Concrete shows good resistance to cyclic freezing and thawing and deicing salts when the diameters of the air pores are 300–3000 nm, and the distribution index is not more than 0.2 mm [4, 7, 8, 9]. The increased volume of pores in the range of 350–2000 nm was considered to be responsible for the improved frost resistance durability [10]. Requirements norm for chemical admixtures for concrete EN 934-2 [11] limit the air content in the mixture as a result of the superplasticizer action. The volumetric air content of the modified mixture may be a maximum of 2% higher than the control mixture. In case of self-compacting mortars and concrete, the air entrainment of the concrete mixture, as well as adequate values of porosity structure parameters, are the problematical issues of concrete mixture self-compaction [12–17]. The excessive air-content is mainly caused by lowering the surface tension of the liquid phase into the slurry by the PCP superplasticizer [17]. During intense mixing of a concrete mixture with the addition of the new generation superplasticizer, the air content can increase too high so that better concrete properties achieved by reducing the w/c ratio can be completely lost [7]. That is why producers of the admixtures use antifoaming agents (AFA) to limit the undesirable amount of air in the concrete mixture. However, we struggle with the problem of compatibility and stability of PCP-AFA system. The components of AFA could be mineral oils, silicone oils, organically modified silicones, hydrophobic constant molecules (silica, waxes, higher fatty acids soaps, alcohols and fatty acids), emulsifiers, polyalcohol, or alcohol derivatives of organic compounds. Mixtures of mentioned above active components could have a synergetic effect. Unfortunately, high price and insufficient recognition of the influence on the fresh mixture and concrete properties do not favour wider use of the anti-foaming admixtures. Defoaming substances are chemical compounds aimed at destroying foam or preventing its formation. There are thousands of different skimmers in the world. The detailed composition of defoaming agents is known only to manufacturers. The most efficient defoamers show synergistic action of the hydrophobic liquid and solid phase. Effectiveness of defoamers depends on many factors: – solubility – most of the defrosting admixtures have very low solubility in aqueous solutions; – the size of the defoamer drops – the force needed by the defoaming subunit to destroy the wall of the air bubble increases with the decreasing size of the drop; – the presence of hydrophobic solids – mixtures of liquids with solid bodies are usually more effective than each of the components used alone; – repeated foam exposure – continuous foam exposure eliminates the ability of a defoamer to inhibit foam formation. This is probably due to the hydrophobic molecule separation and too high reduction in the size of the skimmer droplet; – the concentration of surfactants – a higher concentration of surfactants leads to a reduc-tion in the effectiveness of antifoaming agent by increasing the force needed to overcome the interfacial membrane; – shear forces – they have significant effects on the defoamer operation. High shear forces reduce the size of the perspiration drops, which become too small to break up the wall of the air bubble so that it is less effective. In addition, shear forces cause intense foam formation; – viscosity – the viscosity of a defoamer affects the ease of its dispensing and dispersion in the desired medium [31]. The papers [18, 19, 20] compare four different chemical compositions of antifoaming products, mineral oil polyetheremulsified silicone oil and Polyether modified silicone respectively. The bubble breaking speed, restraining bubbles ability and bubbles stability are different when adding different types of defoaming agent. According to the comprehensive performance of concrete, the fluidity of concrete with the addition of the polyether-modified silicone antifoaming agent is the best. The fresh concrete 62 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 4/2019 T H E I N T E R A C T I O N S B E T W E E N A N T I F O A M I N G A N D S U P E R P L A S T I C I Z I N G A D M I X T U R E S . . . slump, expansion and the density fluctuate less than other types of antifoaming agent. Concrete slump loss was also less than other types of antifoaming agent, at the same time, hardened concrete apparent has no obvious harmful pore. The incorporation of AFA decreases the coarse pore content ( 100 nm) and air bubbles with a diameter bigger than 100 μm in the hardened specimen, is playing a positive role in optimising the pore structure and improving strength. The bubbles’ size, number and distribution have a significant effect on the workability, and strength of mortar and concrete. In practical engineering application, we always add an anti-foaming agent to eliminate harmful bubbles. There are many different kinds of an anti-foaming agent, and this paper mainly studies six different kinds of them and their influence on self-compacting mortar and concrete. Moreover, the compatibility of AFA and PCP is important to obtain the expected AFA effect. In the paper, tests results of compatibility of six types of AFA and two types of PCP, the influence of time and type of introduction, from AFA to mortar, and its influence on consistency and air-content of mortar and mixture, compressive strength, the porosity of hardened concrete and its hardened microstructure are analyzed. 2. RESEARCH METHODOLOGY 2.1. Research methodology of compatibility tests of PCP and AFA admixtures The first of the above tests allows assessing the homogeneity of the ready admixture during its storage. Uniformity is one of the basic features of mortar and concrete admixtures, which is subjected to quality control in accordance with Table 1 in EN 934-1. The test itself consists of placing the prepared admixtures in the oven at 40°C for seven days. Increased temperature causes the acceleration of ageing processes. After one week, the visual stability of the domes is assessed. 2.2. Research methodology of type of AFA and PCP types and ways of its introduction on properties of mortars The effectiveness of anti-foaming admixture (Table 1) depending on its type and SP type (Table 2) was investigated in tests of flow and air-entrainment of mortar according to EN 1015-3:2000/A2:2007 [21] and EN 1015-7:2000 [22], respectively. Self-compacting mortars were composited with river sand 0–2 mm. PCP1 is synthesized with long side chains. PCP2 has a rapid absorption to the cement particles and covers less surface, which ensures a large surface of cement particles to react with water and then accelerates the cement hydration. The process of mixing of the mortars started with dry ingredients. Then the PCP were added: – at the same moment as superplasticizer or – after 10 min from induction of superplasticizer to mortar. The mixing of mortars components was carried out in accordance with the procedure of PN EN 480-1 [23]. The cement CEM II/B-S was used because previous author’s research result indicated that most problems with adequate air-content of self-compacting mortar and concrete are in case of cement with mineral additives, like fly ash or granulated blast furnace. The properties of the mortars were described by density, tested in accordance with EN 1015-10:2001 [24] standard, compression and flexural strength tested according to EN 1015-11:2001 + A1:2007 [25]. To assess AFA influence on the time relating to workability loss of the mortar, the assessment of mortar flow was measured after 10 and 60 minutes, counting from the time of components mixing. All tests of hardened mortars were carried out after 28 days on 4 4 16 cm mortar blocks curing in 20°C water. C I V I L E N G I N E E R I N G ce 4/2019 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 63 Table 1. AFA components Symbol of AFA (A) AFA characteristic A1 froth breaker based on PDMS / silicone oil / hydrophobic silica A2 froth breaker based on mineral oil or amidol wax A3 froth breaker based on alcohol derivative of saturated fatty alcohol, mineral oil and PE wax A4 fiakyl derivative of saturated fatty alcohol/mineral oil/PE and amidol wax A5 alkoxyl derivative of fatty alcohol A6 polyether modified silicone B . Ł a ź n i e w s k a P i e k a r c z y k 2.3. Research methodology of AFA and PCP on properties of self-compacting concrete In next step of the research, self-compacting concrete

THE INTERACTIONS BETWEEN ANTI-FOAMING AND SUPERPLASTICIZING ADMIXTURES AND THEIR CONSEQUENCE FOR PROPERTIES OF SELF-COMPACTING MORTAR AND CONCRETE