13
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
Table 1: Chemical composition of AACs components.
Component
Oxides, % by mass
LOI
SiO
2
Al
2
O
3
Fe
2
O
3
MnO MgO CaO N
2
O SO
3
clinker 21.30
5.70
4.62
-
1.20
65.90
0.30
0.86
0.12
slag 39.00
5.90
0.30
0.50
5.82
46.94
-
1.54
-
Soda ash (Na
2
CO
3
) and sodium metasilicate pentahydrate (Na
2
SiO
3
5
2
O) were used as
alkaline components. In the production of the AACs under "all- in- one" technology (alkaline
components in the form of solids) it is required to use sodium lignosulfonates (further, LST)
in order to provide the required setting times and strength. In order to intensify a grinding
process and to prevent sorption of moisture from air and preserve properties of the AAC an
admixture of ethyl hydro-siloxane polymer was also used.
The AAC compositions are shown in Table 2. Fineness of the AACs (measured as specific
surface by Blaine) was 4500 cm
2
/g. The contents of alkali metal compounds (alkaline
activators) were taken over 100% of the aluminosilicate components in accordance with [13].
In order to change a consistency of the AAC concrete mixtures from class S1 (that of the
reference composition) to class S4 at ambient temperature of 20±2 ºC, complex admixtures
(further, CA) based on LST in combination with corresponding plasticizing admixtures (taken
in quantities of 1.5% by the AAC) were used.
The plasticizing admixtures varied in nature of main active substances: 1 – surfactant based on
polyacrylate esters, Type PA (traditional superplasticizer "Dynamon SR 2”, Mapei); 2 -
surfactant based on polyethers (polyethylene glycol “PEG-400”, JSC "Barva"); 3 - surfactant
based on sodium gluconate (“Mapetard SD 2000”, Mapei), which is traditionally used as a
retarder.
Table 2: Compositions of the AAC.
# of composition
Basic composition
1
50% slag, 50% clinker, 2% Na
2
CO
3
, 1% LST
2
50% slag, 50% clinker, 3% Na
2
SiO
3
5
2
O, 1% LST
3
69% slag, 31% clinker, 2,5% Na
2
CO
3
, 1% LST
4
69% slag, 31% clinker, 3,5% Na
2
SiO
3
5
2
O, 1% LST
5
88% slag, 12% clinker, 3% Na
2
CO
3
, 1% LST
6
100% slag, 4.7% Na
2
CO
3
, 0.8% LST
In these studies in order to determine the influence of variables (cement composition and
nature of main active substance of admixtures) on capillary porosity and freeze/thaw
resistance of the AAC concrete, one cement composition was chosen. The standard
composition of the AAC concrete was taken in accordance with [14], kg/m
3
: cement - 350;
silica sand - 740; granite gravel: 330 (5/10) and 780 (10/20).
Water absorption and porosity of the AAC concretes were studied in accordance with
methodology of the national standard of Ukraine [15]. According to this method, the concrete
cubes (100 mm) after 28 days were dried up to a constant weight at t= 105±10 °C. Then, the
14
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
specimens were saturated with water until a constant weight would be obtained at t= 20±2 °C.
The values of porosity were calculated from the values of average density and water
absorption of the concrete specimens.
Freeze/thaw resistance was studied in accordance with third test method prescribed by the
national standard of Ukraine [16]. According
to this accelerated method, the concrete cubes
(100 mm) were saturated with a 5% solution of NaCl at t= 18±2 °C and after that were
subjected to freezing at t= -50 °C. Thawing was done in a 5% solution of NaCl. A class of
concrete in freeze/thaw resistance was designated as a number of alternate freezing and
thawing at which a mean compressive strength decreased by no more than 5%. The
freeze/thaw resistance of concrete was assessed by the correspondence between permissible
number of freezing-thawing cycles on the used accelerated method and on first (basic) method
prescribed in mentioned standard.
3. Research
results
As a result of the study a conclusion was drawn that changes in slag contents, type and
content of alkaline component affected porosity and consequently freeze/thaw
resistance of
the AAC concrete depending on the nature of main active substance of plasticizer.
The use of polyester - based CA in the AAC concretes containing 50% of slag and 2% of soda
ash (composition #1) lead to slight increase in water absorption and open capillary porosity of
the AAC concretes (Fig. 1; Fig. 2) to 3.7% and 8.8%, respectively, compared to those of the
reference composition: water absorption of 3.4% and volume of open capillary pores of 8.1%.
a) b)
Figure 1: Water absorption of the AAC concretes vs. type of surfactants as ingredient of CA
and slag contents in the AACs, % (see Table 2): a) #1, #3, #5, #6; b) #2, #4.
With increase in slag contents in the AACs up to 88% the effectiveness of modification of the
AAC concretes by this CA tended to significantly decrease and was accompanied by decline