Building mortars on sulphate-and-slag basis

Dvorkin O.L., doctor of technical sciences, professor,

Kundos M.G., post-graduate student

National University of Water Management and Natural Resources Use

Rivne, Ukraine

BUILDING MORTARS ON SULPHATE-AND-SLAG BINDING BASIS

Nowadays new effective building materials become more and more urgent. Decreasing of building materials energy capacity is one of most urgent problems in building. Wide usage of local materials and industrial waste can help to solve the problem. It can improve ecological condition and diminish harm of building materials production. In binding materials production waste-products of metallurgy are widely used, especially blast furnace slag. Producing of concretes on the effective binding basis results in much lower energy consumption and rather high technical properties compared with traditional portlandcement concrete.

There are different slag binding materials without cement. Sulphate-and-slag binding is one of them.

Sulphate-and-slag binding (SSB) is a hydraulic binding made by combining milling of blast slag (80…85%) sulphatic activator (10…15%) and small quantity of portlandcement (less than 5%).

It is known that SSB utilization is very effective for producing materials and constructions with special requests of sulphatic resistance or resistance to acids and oil products [1, 2]. Regardless of long term of knowing SSB (technology of its producing was developed at the beginning of 20th century by P.P.Budnikov), we think that its potential is not completely revealed. New modern chemical admixture modifiers and methods of sulphate-and-slag binding activation allow increasing considerably effectiveness of SSB and to lower energy capacity and building costs.

For conducting investigations we produced SSB by mixing fine-grained blast furnace slag of metallurgical industrial complex of Kryvyi Rih, portlandcement M500 PC-II/A “Volyncement” PLC and sulphatic activator. The influence of the following kinds of sulphatic activators was investigated: building gypsum (BG) G-5, dumped phosphogypsum (PG) of Rivne PLC “Azot” and phosphogypsum binding (PGB) that was made by neutralization of grained phosphogyps. Quartz sand with fineness modulus М_F = 1,2 was used as a filler.

Series of vibropressed beam-shaped examples of mortars with dimensions 40x40x160 mm were produced for research. We changed correlation SSB:sand (binding:sand) from 1:1 till 1:3 to investigate sand content influence to strength in different terms. The strength of examples was studied at age of 7, 28 and 60 days. All series of examples with different kinds of sulphatic activators hardened in identical temperature and moisture conditions, which is above water at temperature 20±2°С.

All researches were conducted using mathematical planning methods of experiments. Plasticity was determined by cone flowing and is between 120 and 150 mm. Experiments were conducted according to three-level plan for two factors. The conditions of factors variation are shown in table 1.

Table 1

Terms of factors variation

Factors		Levels of variation			Interval of variation
In kind	Encoded	-1	0	1	Interval of variation
Water, l/m³	Х₁	257	278	299	21
Water/Binding	Х₂	0,3	0,4	0,5	0,1

Compression strength and bending strength of mortars on SSB basis was determined at the age of 7, 28 and 60 days. Statistic processing of test results allows getting mathematical regression equation that connects proper indices of strength and factors.

Regression equation is generally shown as:

, (1)

where R – index of mortar strength; – empirical coefficients.

Value of empirical coefficients of regression equations for compression and bend strength of different age examples are shown in the table 2.

Table 2

Value of coefficients in the equation (1)

Activator	Studied parameter	Coefficients
Activator	Studied parameter	b₀	b₁	b₂	*b₁₁*	*b₂₂*	*b₁₂*
1	2	3	4	5	6	7	8
Building gyps	Compression strength at age of 7 days	8,543	0,600	-1,650	-0,028	-0,478	0,075
	Compression strength at age of 28 days	14,506	1,067	-3,067	0,353	-0,547	0,175
	Compression strength at age of 60 days	17,881	1,284	-3,734	0,157	-0,993	0,400
	Bending strength at age of 7 days	4,325	0,617	-1,351	-0,486	-0,386	-0,375
	Bending strength at age of 28 days	5,868	0,733	-1,684	-0,442	-0,692	-0,325
	Bending strength at age of 60 days	6,639	0,483	-1,934	-0,795	-0,445	-1,151
Phosphogypsum binding	Bending strength at age of 7 days	3,729	0,518	-0,930	-0,145	0,020	-0,505
	Bending strength at age of 28 days	6,002	0,650	-1,424	0,534	-1,156	-0,570
	Bending strength at age of 60 days	6,389	0,676	-1,881	0,326	-0,985	-0,194
	Compression strength at age of 7 days	10,086	1,282	-1,817	0,611	-0,224	-0,295
	Compression strength at age of 28 days	17,305	1,567	-3,701	1,252	0,052	0,250
	Compression strength at age of 60 days	20,989	1,460	-4,893	1,973	-0,452	0,655
Dumped phosphogypsum	Bending strength at age of 7 days	3,116	0,357	-0,930	-0,038	-0,178	-0,090
	Bending strength at age of 28 days	3,252	0,485	-1,044	0,011	0,336	-0,048
	Bending strength at age of 60 days	4,200	0,347	-1,067	-0,047	0,313	-0,060
	Compression strength at age of 7 days	7,538	0,590	-1,555	-0,260	-0,355	0,075
	Compression strength at age of 28 days	11,077	1,475	-2,120	0,348	0,563	-0,533
	Compression strength at age of 60 days	13,169	1,294	-2,512	0,169	0,384	-0,118

The analysis of researches showed that the greatest compressive strength (R_c) of mortars on SSB basis examples was reached using phosphogypsum binding as sulphatic activator (near 25 Mpa at age of 28 days and 30 Mpa at age of 60 days for mortars with binding:sand ratio equal 1:1). Less effective activator is dumped PG. With its use compression strength of mortars with same binding:sand ratio at age of 28 days was 16 Mpa and at age of 60 days – 18 Mpa. Intermediate results were got with use of BG as sulphatic activator.

Fig.1. Compressive strength change of SSB mortar examples under filler content change when building gypsum is used as activator.

Fig.2. Compressive strength change of SSB mortar examples under filler content change when phosphogypsum binding is used as activator.

Dynamics of strength change in time for mortars with different sand content is shown at figures 1-6.

Fig.3. Compressive strength change of SSB mortar examples under filler content change when dumped phosphogypsum is used as activator.

Fig.4. Bending strength change of SSB mortar examples under filler content change when building gypsum is used as activator.

Fig.5. Bending strength change of SSB mortar examples under filler content change when phosphogypsum binding is used as activator.

Fig.6. Bending strength change of SSB mortar examples under filler content change when dumped phosphogypsum is used as activator.

As shown at figures 1-6, mortars on SSB basis with all kinds of sulphatic activators tend to have some strength decrease with growth of sand quantity.

When PGB was used as activator, compression strength at age of 60 days for mortars with binding:sand ratio equal 1:1 was 28…30 Mpa, with binding:sand ratio equal 1:3 – 16…18 Mpa. Under use of BG as sulphatic activator compression strength at age of 60 days for mortars with binding:sand ratio equal 1:1 was 22…24 Mpa, with binding:sand ratio equal 1:3 – 10…12 Mpa. When dumped PG was used as activator, compression strength at age of 60 days for mortars with binding:sand ratio equal 1:1 was 16…18 Mpa, with binding:sand ratio equal 1:3 – 8…10 Mpa.

Fig.7. Comparison of compressive strength growing of SSB mortars with SSB:Sand correlation 1:1 using different kinds of activators.

Fig.8. Comparison of compressive strength growing of SSB mortars with SSB:Sand correlation 1:2 using different kinds of activators.

It is necessary to point out that for different kinds of activators tendency of building mortars strength growth in time was observed (figures 7-9).

Fig.9. Comparison of compressive strength growing of SSB mortars with SSB:Sand correlation 1:3 using different kinds of activators.

The researches of strength of building mortars on sulphate-and-slag binding basis using different kinds of sulphatic activators show that utilization of such binders allows reaching sufficient strength indices for producing different building articles. Strength compressing changes from 30 Mpa till 15 Mpa depending on sand content in building mortars. The possibility of building mortars quality improvement by utilization of industrial waste, exactly phosphogypsum binding, is shown. Building mortars on SSB basis have ability to increase strength persistently in the course of time. They can successfully replace articles made from portlandcement in individual cases.

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