Proceedings of the International rilem conference Materials, Systems and Structures in Civil Engineering 2016

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International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

in properties, i.e. higher water absorption (up to 4.7%) and volume of open capillary pores (up 

to 11%). 

 

a)                                 :                                 b)

 

                                  a)                                    :                                    b)

 

Figure 2: Volume of open capillary pores (I) and conditionally closed pores (II) of the AAC 

concrete vs. type of surfactant as ingredient of  CA and  slag  contents  in the AACs, % (see 

Table 2): a) #1, #3,#5, #6; b) #2, #4. 

 

Substitution of anionic part of alkaline component from carbonate to silicate resulted in the 

higher values of water absorption and porosity of both reference and modified AAC 

concretes. For example, when used AAC with slag content of 50% (composition #1) water 

absorption and volume of open capillary pores was 3.4% and 8.1% respectively. When soda 

ash was changed with sodium silicate pentahydrate (composition #2) the water absorption and 

the volume of open capillary pores of concrete increased to 3.7% and 9.0% respectively. 

 

At the same time, there was observed a general tendency to reduction of volume of the open 

capillary pores of the reference AAC concretes with increase in slag contents and, 

accordingly, with increase in the required alkaline component contents of the AACs (Fig. 2).  

This fact can be attributed to changes taking place in pore structure towards the formation of 

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16

International RILEM Conference on Materials, Systems and Structures in Civil Engineering 

Conference segment on Service Life of Cement-Based Materials and Structures 

22-24 August 2016, Technical University of Denmark, Lyngby, Denmark 

 

micro- and conditionally closed pores which determine the formation of more dense and 

impermeable concrete structure with simultaneous increase of its performance properties. 

 

Modification of the AAC concretes by addition of polyester-based admixtures in case of the 

AAC compositions #1 and #3 (50% of the slag) provided class F200 in freeze/thaw resistance 

(Fig. 4), i.e. highest class for the most demanding concrete structures in unheated buildings 

undergoing alternate freezing-thawing and operating at ambient temperature t = -20...-40 ° C 

(exposure class XF4). However, with increase in slag contents up to 69% the efficiency of 

modification by this admixture tended to decrease: the volume of capillary pores increased 

(up to 9.6%) and freeze/thaw resistance declined (class F150). 

 

Therefore efficiency of the admixture Type 1 as ingredient of CA in the AAC concretes 

depends on the AAC composition. At slag contents up to 50% and with corresponding 

concentration of alkaline component the CA provided changes in consistency of the AAC 

concrete mixtures from S1 to S4 class with maintaining physical properties of the AAC 

concretes nearly at the level of the reference composition and without decline of freeze/thaw 

resistance. However, the increase in slag contents up to 88% in the AACs resulted in decrease 

in efficiency of the mentioned CA: deterioration of pore structure and decline of freeze/thaw 

resistance. 

 

The use of polyethylene glycol as ingredient of CA in case of the AACs containing 88% of 

slag did not significantly affect pore structure of the resulted concrete (Fig. 1, Fig. 2). Water 

absorption increased from 3.1% to 3.3% and porosity from 7.4% to 7.8%, respectively, as 

compared to those of the reference composition. This helped to obtain a dense structure of the 

plasticized AAC. The admixture of this type as ingredient of CA with the AAC composition 

#5 (88% of slag) provided class F 200 freeze/thaw resistance for the AAC concrete (Table 3). 

With increase in slag contents in the AAC up to 100%, structure indexes of the AAC 

concretes did not significantly change: water absorption increased from 3.0% (of the reference 

composition) to 3.2%; the quantity of open capillary and conditionally closed pores increased 

from 7.3% to 7.7% and from 2.4% to 2.8%, respectively. This allowed obtaining the modified 

AAC concretes containing 100% of slag (composition #6) with class F200 in freeze/thaw 

resistance (Table 3) due to additionally generated artificial air pore volume. 

 

Substitution of soda ash by sodium metasilicate pentahydrate as alkaline component of the 

AACs leads to the higher values of water absorption and open capillary porosity of the 

modified AAC concretes. With slag contents of 50% in the AACs water absorption tended to 

increase from 3.3% (composition #1) to 3.5% (composition #2); the volume of open capillary 

pores tended to increase from 7.9% to 8.4%, respectively. A similar trend was observed with 

the increase in slag contents in the AAC up to 69%: water absorption of the modified AAC 

concrete was 3.2%, with sodium metasilicate pentahydrate in the AAC cement (composition 

#4) – 3.9%, volume of open capillary pores of the modified AAC concrete was 7.7%, with 

sodium metasilicate pentahydrate in the AAC (composition #4) – 9.2%. 

 

Thus, in contrast to the polyester-based CA the effect from the polyether-based CA on 

plasticizing and formation of the concrete pore space  increased proportionally to the growth 

in slag contents and, correspondingly, in alkaline component content in AAC. 

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