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

11

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 

 

IMPACT OF SLAG CONTENT IN ALKALI-ACTIVATED SLAG 

CEMENT ON POROSITY OF CONCRETE 

 

Pavel Krivenko

(1)

, Oles’ Lastivka

(1)

, Igor Rudenko

(1)

, Sergei Lakusta

(1)

  

 

(1) Kyiv National University of Construction and Architecture, Scientific Research Institute 

for Binders and Materials, Ukraine 

 

 

 

 

 

 

Abstract 

The paper covers results of studies on porosity, freeze/thaw resistance of alkali-activated slag 

cement (AAC) concrete depending upon composition of AAC and chemical admixtures. 

Freeze-thaw resistance was assessed by a number of cycles of alternate freezing/thawing in 

aqueous solution of NaCl at t= - (50 ± 5) °C until 5% loss of compressive strength. This 

strength loss can be attributed to accumulation of deteriorations caused by cyclic volume 

deformations occurred in concrete structure in the process of ice formation. With increase of 

slag content in AAC from 50 to 100% and corresponding increase of alkaline component 

content a volume of open capillary pores tended to decrease with formation of more quantities 

of micro- and conditionally closed pores. Effect of polyethers as admixtures was greater, 

whereas, effect of polyesters was “suppressed”. Change of alkaline component from sodium 

carbonate to sodium silicate in AAC resulted in increase of concrete porosity. With reduction 

of volume of open capillary pores the volumes of ice formed in the AAC concrete tended to 

decrease, similar to stresses which could cause changes in the AAC concrete structure, thus 

“spoiling” its freeze/thaw resistance. 

 

 

1. Introduction 

 

A  need in alternative types of cements is explained by the fact that portland cement is 

characterized by high consumption of natural resources and energy, accompanied by carbon 

dioxide emissions [1]. 

 

The use of ground granulated blast furnace slag allows for not only reducing energy 

consumption in cement production. Blast furnace cement has several advantages over 

portland cement: high resistance in soft and sulfate waters, high heat resistance, low heat of 

hydration (low heat cement) and shrinkage [2, 3]. However, concretes made from the cements 

with high slag contents (blast furnace cement) are characterized by low early strength and are 

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12

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 

 

sensitive to attacks of freeze/thaw resistance, especially under exposure of de-icing salt 

solutions. 

 

One of the ways to avoid these disadvantages is to add to traditional blast furnace cement the 

alkali metal compounds in order to produce alkali-activated slag cement (further, AAC) the 

hydration products of which provide high strength and density of the resulted cement stone 

and to minimize contents of portland cement clinker in the cements [4, 5, 6]. 

 

A key factor of physical nature which determines performance properties and durability of 

concrete is its porosity. However, if strength of concrete depends on a total porosity, 

freeze/thaw resistance and durability are determined chiefly by a capillary porosity. The 

reason for these phenomenons is the effect of capillary pores, which is caused by dependence 

of a freezing point from pore size [7].

  

 

In general, the incorporation of alkali metal compounds into the blast furnace cement shifts of 

ratio between macro- and micro-porosities towards the formation of micro- and conditionally 

closed pores, resulting in higher freeze/thaw resistance of concrete [8]. In this case, in order to 

make concrete technology simpler, and to obtain better performance properties, the use of 

plasticizers is a necessity. However, plasticizers that are traditionally used in making portland 

cement concretes are not suitable for the alkali-activated cement concretes because in the 

alkali-activated cement matrix they behave in a different way and an alkaline medium causes 

degradation of traditional plasticizers [9, 10, 11]. 

 

The results of study held on various plasticizers in the AAC concretes are reported in [12]. 

These results can be explored for a choice of chemical nature of main active substance of 

plasticizers to be suitable for the AAC concretes depending upon slag contents and, 

accordingly, contents of alkaline component. 

 

The purpose of this study was to reveal an impact of slag contents in the AAC on water 

absorption, open capillary porosity and conditionally closed porosity of the plasticized AAC 

concrete as a function of its freeze/thaw resistance. 

 

 

2.  Raw materials and testing techniques  

 

The alkali activated cements varying in slag contents between 50 and 100% as per national 

standard of Ukraine were used [13]. 

 

Ground granulated blast furnace slag (further, slag) and portland cement clinker (further, 

clinker) were used as aluminosilicate components of the AACs, their chemical compositions 

are shown in Table 1. The comparative low content of glass phase in slag (56%) was in 

accordance with [13] and can be explained by high basicity modulus of slag (M

b

 = 1.1)  

 

 

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