3.5 Sulphate resistance

Basic physical properties and standard strengths are summarized in Table 10. HC compared to PC is characterized by low C3A content. Such composition predisposes such cement to be chemically more resistant than PC. Properties of fresh mortars are listed in Table 11. HC mortar compared to both reference is characterized by the higher specific surface area and standardized density. In spite of that


#### Table 9.

Prediction of andesite susceptibility to ASR by the chemical test.

Figure 3. Length changes of the mortars with the ASR aggregate andesite.

Fundamental Properties of Industrial Hybrid Cement Important for Application in Concrete DOI: http://dx.doi.org/10.5772/intechopen.88060

fact, water-to-cement ratio of HC mortar is 0.42 compared to 0.5 of PC mortar when both are adjusted on the same consistency of 140 1 mm. H-Cement shows plasticity effect in the mortar; however, it is unable to reach the strength level of both reference mortars, as reported in Table 10. The second reference mortar was prepared from C3A-free industrially made Portland cement (abbreviated as SR). HC and PC mortars were adjusted on the same consistency; that of SR differs. SR and PC were produced with the same w/c ratio of 0.5.

Chemical composition of PC and HC mortar after 28-day basic curing in water at (20 1)°C is listed in Table 12.

The cements confirm a substantial difference, especially in CaO content, also evident in Al2O3 and detectable in Na2O eq. amounts. Low CaO in hybrid cement is a prerequisite for the increased chemical resistance. Higher levels of Al2O3 and Na2O eq., as opposed to PC mortar, induce the occurrence of the alkali-activated binder based on pozzolanic components as an inorganic polymer characterized by a binder potential alongside the minor portion of hydrated PC clinker.

Dynamic modulus of elasticity (DME) of mortars after 5 years of exposure in the sulphate and water environment is shown in Figure 4. No evident changes were


#### Table 10.

for the tests. The alkali content expressed as Na2O equivalent in both cements was estimated. From this content, the amount of NaOH required to achieve the desired Na2O eq. (1.30 + 0.05)% wt. by the standard was calculated. The tap water was enriched with a calculated amount of NaOH during laboratory production of the mortars. Prediction criteria of andesite aggregate susceptibility to ASR are given in Table 9. The composition of mortars for 6-month length change test cured at 20 and 40°C/100% RH moist air took into account the requirements of the above

The results show that H-Cement is characterized by ASR-mitigating property. H-Cement mortar (abbreviated as HC 20 and HC 40), in contrast with PC (abbreviated as PC 20 and PC 40), clearly reduces the expansion markedly below the maximum allowable standard limit [16] of 0.1% (<1%) regardless of the long-term treatment. ASR-mitigating effect under maximum allowable limit of 0.1% (<1%) is confirmed also for the blended cement consisting of 70% wt. PC and 30% wt. HC

The contemplated cause of ASR mitigation is the presence of alkali-activated pozzolans in the substitution of up to 80% by weight of the PC clinker, which could prevent the expansion [31]. The cause of ASR is a complicated problem and is still not fully understood. In this research focused on the need for industry, the achieved

Basic physical properties and standard strengths are summarized in Table 10. HC compared to PC is characterized by low C3A content. Such composition predisposes such cement to be chemically more resistant than PC. Properties of fresh mortars are listed in Table 11. HC mortar compared to both reference is characterized by the higher specific surface area and standardized density. In spite of that

> Criterion for R value in [16]

Andesite 132.42 400.04 R > 70 S > R Yes

Criterion for S value in [16]

Assumption that aggregate contains reactive forms of SiO2

standard. Length changes are illustrated in Figure 3.

(abbreviated as HM 20 and HM 40 in Figure 3).

3.5 Sulphate resistance

Compressive Strength of Concrete

Aggregate Loss of

Table 9.

Figure 3.

136

alkalinity R (mmol/l)

effect was investigated, and its cause is not studied in detail.

Molar concentration of SiO2 S (mmol/l)

Prediction of andesite susceptibility to ASR by the chemical test.

Length changes of the mortars with the ASR aggregate andesite.

Basic properties of the cements.


#### Table 11.

Properties of fresh mortars.


#### Table 12.

Differences in chemical composition of PC and HC mortar after basic curing.

#### Compressive Strength of Concrete

observed in 5% wt. Na2SO4 for HC and SR mortar, while drops in DME values are found for PC mortar, slightly after 2-year exposure and dramatically after 3-year attack. Elasticity modules at the water curing remain approximately the same.

The effect of sulphate action on the expansion of the mortars is depicted in Figure 5. The HC and SR mortar show negligible expansion in sulphate exposure. PC mortar is specified by negligible length changes underwater, while evident expansion is observed in the sodium sulphate.

Flexural and compressive strength of PC mortar is 9.0 and 63.9 MPa after 4-year curing in water; contrary evident destruction is observed in the sodium sulphate. Determination of the strength was therefore impossible. Excellent resistance of H-Cement to sulphate attack is demonstrated by 5-year strength of HC mortar. Data in Table 13 show that only a slight decrease in flexural and compressive strength is observed between reference water and aggressive sulphate exposure.

that is not sensitive to sulphate attack as well as CEM I 42.5 R-SR 0 but not for the same reason. The cause of high sulphate resistance of H-Cement is explained later. It is approved in Table 14 that PC mortar is characterized by extremely high bound SO3 and ignition loss values after 4-year exposure in 5% wt. Na2SO4 opposite to HC and SR mortar. The CaO content is dramatically reduced in sulphate exposure as compared to that of HC and SR mortar. HC mortar behaves in the sodium sulphate as well as SR mortar; even the difference between the SO3 bound in HC

Flexural Compressive

Qualitative and quantitative differences in mineral and phase composition of PC and HC mortar after 28-day basic curing (BC) in (20 1)°C water are recognized in Figures 6–9. The basic feature of the difference in the mineral composition of both mortars lies in the absence of portlandite Ca(OH)2 in the mortar with the hybrid cement. Hydrated hybrid cement without the developed Ca(OH)2 assumes a realis-

The results of thermal analysis confirmed that H-Cement generates a hydrated

Mineral and phase compositions of the long-term exposed mortars are given in Figures 10–14. PC mortar in water contains quartz SiO2 (Q) from the standardized sand and calcium hydroxide Ca(OH)2 (CH) as a reaction product of cement hydration, also calcite CaCO3 (Cc) as minor mineral. The high content of gypsum CaSO4.2H2O (G) and, to a less extent, more voluminous ettringite 3CaO.Al2O3.3. CaSO4.32H2O (E) are detected in 4-year-old PC mortar exposed to 5% wt. Na2SO4 solution. Contrary, 5-year-old SR mortar shows a reduced content of CH in the sodium sulphate compared to water exposure and only a slight indication of the presence of CaSO4.2H2O arising as a reaction product of sulphate attack. HC mortar records in the same time negligible differences in mineral composition. The presence of CH and any reaction products of sulphate attack (G and E) are not confirmed; a negligible share of the marginal sodium thiosulfate pentahydrate Na2S2O3.5H2O (SH) and mirabillite Na2SO4.10H2O (MI) is detected. Both of the latter minerals would be considered as reaction products of sulphate attack, however, with no negative impact on degradation of the mortar. TG-DTA plot confirms the presence of reaction products of sulphate attack in PC mortar by endotherm with maximum peak at 160°C (Figure 13), compared to HC mortar (Figure 14). The presence of CH was not recognized in HC mortar in water and Na2SO4 exposure. The minimum presence of calcite CaCO3 (Cc) is also negligible in terms of

Basic parameters of the pore structure of the mortars are considered in Table 15. PC mortar is characterized by evident coarsening of the pore structure after 4 years of exposure to the sodium sulphate. This finding is proven by one order of increased permeability in contrast to water treatment. HC and SR mortars show no significant differences in the pore structure parameters after 5 years of exposure. The insignificant detrimental effect of 5-year sulphate attack on HC and SR mortar is also proven by the permeability values, which remain for each mortar the

phase without the formation of crystalline Ca(OH)2. This fact can decisively

mortar in sulphate and water exposure is smaller than that in SR mortar.

HC mortar kept in Strength (MPa)

HC mortar strength characteristics at 5-year age from the production in 2012.

DOI: http://dx.doi.org/10.5772/intechopen.88060

Reference water 9.1 47.1 Aggressive 5% Na2SO4 6.7 44.8

Fundamental Properties of Industrial Hybrid Cement Important for Application in Concrete

tic chemical resistance in terms of sulphate resistance.

mortar damage.

139

Table 13.

improve the increase in resistance to sulphate aggressiveness.

The structural integrity of SR and HC mortar is not disturbed, despite the found slight differences between the 5-year strength parameters. The observed HC mortar's sulphate resistance is determined by the material composition of H-Cement

Figure 4. Changes in DME of mortars in 5% Na2SO4 solution and water over time.

Figure 5. Length changes of mortars in 5% Na2SO4 solution and water over time (1 mm/m = 1%) = 0.1%.


Fundamental Properties of Industrial Hybrid Cement Important for Application in Concrete DOI: http://dx.doi.org/10.5772/intechopen.88060

#### Table 13.

observed in 5% wt. Na2SO4 for HC and SR mortar, while drops in DME values are found for PC mortar, slightly after 2-year exposure and dramatically after 3-year attack. Elasticity modules at the water curing remain approximately the same. The effect of sulphate action on the expansion of the mortars is depicted in Figure 5. The HC and SR mortar show negligible expansion in sulphate exposure. PC mortar is specified by negligible length changes underwater, while evident

Flexural and compressive strength of PC mortar is 9.0 and 63.9 MPa after 4-year curing in water; contrary evident destruction is observed in the sodium sulphate. Determination of the strength was therefore impossible. Excellent resistance of H-Cement to sulphate attack is demonstrated by 5-year strength of HC mortar. Data in Table 13 show that only a slight decrease in flexural and compressive strength is

The structural integrity of SR and HC mortar is not disturbed, despite the found slight differences between the 5-year strength parameters. The observed HC mortar's sulphate resistance is determined by the material composition of H-Cement

observed between reference water and aggressive sulphate exposure.

Changes in DME of mortars in 5% Na2SO4 solution and water over time.

Length changes of mortars in 5% Na2SO4 solution and water over time (1 mm/m = 1%) = 0.1%.

expansion is observed in the sodium sulphate.

Compressive Strength of Concrete

Figure 4.

Figure 5.

138

HC mortar strength characteristics at 5-year age from the production in 2012.

that is not sensitive to sulphate attack as well as CEM I 42.5 R-SR 0 but not for the same reason. The cause of high sulphate resistance of H-Cement is explained later.

It is approved in Table 14 that PC mortar is characterized by extremely high bound SO3 and ignition loss values after 4-year exposure in 5% wt. Na2SO4 opposite to HC and SR mortar. The CaO content is dramatically reduced in sulphate exposure as compared to that of HC and SR mortar. HC mortar behaves in the sodium sulphate as well as SR mortar; even the difference between the SO3 bound in HC mortar in sulphate and water exposure is smaller than that in SR mortar.

Qualitative and quantitative differences in mineral and phase composition of PC and HC mortar after 28-day basic curing (BC) in (20 1)°C water are recognized in Figures 6–9. The basic feature of the difference in the mineral composition of both mortars lies in the absence of portlandite Ca(OH)2 in the mortar with the hybrid cement. Hydrated hybrid cement without the developed Ca(OH)2 assumes a realistic chemical resistance in terms of sulphate resistance.

The results of thermal analysis confirmed that H-Cement generates a hydrated phase without the formation of crystalline Ca(OH)2. This fact can decisively improve the increase in resistance to sulphate aggressiveness.

Mineral and phase compositions of the long-term exposed mortars are given in Figures 10–14. PC mortar in water contains quartz SiO2 (Q) from the standardized sand and calcium hydroxide Ca(OH)2 (CH) as a reaction product of cement hydration, also calcite CaCO3 (Cc) as minor mineral. The high content of gypsum CaSO4.2H2O (G) and, to a less extent, more voluminous ettringite 3CaO.Al2O3.3. CaSO4.32H2O (E) are detected in 4-year-old PC mortar exposed to 5% wt. Na2SO4 solution. Contrary, 5-year-old SR mortar shows a reduced content of CH in the sodium sulphate compared to water exposure and only a slight indication of the presence of CaSO4.2H2O arising as a reaction product of sulphate attack. HC mortar records in the same time negligible differences in mineral composition. The presence of CH and any reaction products of sulphate attack (G and E) are not confirmed; a negligible share of the marginal sodium thiosulfate pentahydrate Na2S2O3.5H2O (SH) and mirabillite Na2SO4.10H2O (MI) is detected. Both of the latter minerals would be considered as reaction products of sulphate attack, however, with no negative impact on degradation of the mortar. TG-DTA plot confirms the presence of reaction products of sulphate attack in PC mortar by endotherm with maximum peak at 160°C (Figure 13), compared to HC mortar (Figure 14). The presence of CH was not recognized in HC mortar in water and Na2SO4 exposure. The minimum presence of calcite CaCO3 (Cc) is also negligible in terms of mortar damage.

Basic parameters of the pore structure of the mortars are considered in Table 15.

PC mortar is characterized by evident coarsening of the pore structure after 4 years of exposure to the sodium sulphate. This finding is proven by one order of increased permeability in contrast to water treatment. HC and SR mortars show no significant differences in the pore structure parameters after 5 years of exposure.

The insignificant detrimental effect of 5-year sulphate attack on HC and SR mortar is also proven by the permeability values, which remain for each mortar the



Figure 6.

Figure 7.

Figure 8.

141

Mineral composition of PC mortar after 28-day basic curing in water.

DOI: http://dx.doi.org/10.5772/intechopen.88060

Fundamental Properties of Industrial Hybrid Cement Important for Application in Concrete

Mineral composition of HC mortar after 28-day basic curing in water.

TG-DTA plots of PC mortar after 28-day basic curing in water.

Fundamental Properties of Industrial Hybrid Cement Important for Application in Concrete DOI: http://dx.doi.org/10.5772/intechopen.88060

Figure 6.

Mineral composition of PC mortar after 28-day basic curing in water.

Figure 7.

Mineral composition of HC mortar after 28-day basic curing in water.

Figure 8. TG-DTA plots of PC mortar after 28-day basic curing in water.

Constituent

140

PC mortar

28-day BC + 4 years in

28-day BC + 4 years in

28-day BC + 5 years in

28-day BC + 5 years in

28-day BC + 5 years in

28-day BC + 5 years in

Na2SO4

10.81

55.67

10.00

13.38

3.87

1.36

1.75

0.01

2.46

H

O2

7.65 68.65

7.50 9.17 2.72 1.05 1.66 0.01 1.51

Na2SO4

19.15 42.98 28.19

1.83 2.51 0.82 4.21 0.03 0.22

H2O

16.97 45.85 30.82

1.83 2.53 0.77 1.01 0.03 0.10

Na2SO4

22.97 50.63

7.52 0.67 1.22 2.26 14.31 0.02 0.05

H

Ignition loss

SiO2 CaO

Al

Fe

O2 3

MgO

SO3 Cl Na O eq. 2

Table 14. Chemical composition

 of PC mortar after 4 years and HC and SR mortar after 5 years of exposure in aggressive 5% Na2SO4 and reference water.

O2 3

O2

10.75 60.81 22.90

0.75 1.40 1.82 1.19 0.03 0.06

Contents of the

constituents

SR mortar

HC mortar

Compressive Strength of Concrete

 (% wt.)

Figure 9. TG-DTA plots of HC mortar after 28-day basic curing in water.

Figure 10.

XRD patterns of PC mortar after 4 years in 5% wt. sodium sulphate and water.

same in both exposure conditions (reference water vs. aggressive sulphate), while that of PC mortar is increased by one order even after 4-year exposure to sulphate attack.

Figure 12.

Figure 11.

Figure 13.

143

XRD patterns of HC mortar after 5 years in 5% wt. sodium sulphate and water.

XRD patterns of SR mortar after 5 years in 5% wt. sodium sulphate and water.

Fundamental Properties of Industrial Hybrid Cement Important for Application in Concrete

DOI: http://dx.doi.org/10.5772/intechopen.88060

TG-DTA plots of PC mortar stored 4 years in 5% wt. sodium sulphate and water.

Visual and microscopy observations support the previous finding that sulphate resistance of H-Cement is the same with that of the sulphate-resistant Portland cement. Visual observations prove that 5-year-old HC mortar is characterized by well-preserved structural integrity, while PC mortar is considerably destroyed in the sodium sulphate after 4 years of exposure (Figure 15).

The gypsum and ettringite presence is confirmed in PC mortar after 4-year exposure in the sodium sulphate, while the same reaction products are not detected in HC and SR mortar after 5-year exposure in Na2SO4 (Figure 16). The property of high non-permeability, which is a consequence of the formed hydrate phase character, is a basic condition for the high chemical resistance of a mortar and, in the conveyed meaning of the word, also a concrete made of the same binder system as that which occurred in 5-year-old HC mortar.

Fundamental Properties of Industrial Hybrid Cement Important for Application in Concrete DOI: http://dx.doi.org/10.5772/intechopen.88060

Figure 11.

XRD patterns of SR mortar after 5 years in 5% wt. sodium sulphate and water.

Figure 12.

same in both exposure conditions (reference water vs. aggressive sulphate), while that of PC mortar is increased by one order even after 4-year exposure to sulphate

The gypsum and ettringite presence is confirmed in PC mortar after 4-year exposure in the sodium sulphate, while the same reaction products are not detected in HC and SR mortar after 5-year exposure in Na2SO4 (Figure 16). The property of high non-permeability, which is a consequence of the formed hydrate phase character, is a basic condition for the high chemical resistance of a mortar and, in the conveyed meaning of the word, also a concrete made of the same binder system as

the sodium sulphate after 4 years of exposure (Figure 15).

XRD patterns of PC mortar after 4 years in 5% wt. sodium sulphate and water.

TG-DTA plots of HC mortar after 28-day basic curing in water.

that which occurred in 5-year-old HC mortar.

Visual and microscopy observations support the previous finding that sulphate resistance of H-Cement is the same with that of the sulphate-resistant Portland cement. Visual observations prove that 5-year-old HC mortar is characterized by well-preserved structural integrity, while PC mortar is considerably destroyed in

attack.

142

Figure 10.

Figure 9.

Compressive Strength of Concrete

XRD patterns of HC mortar after 5 years in 5% wt. sodium sulphate and water.

Figure 13. TG-DTA plots of PC mortar stored 4 years in 5% wt. sodium sulphate and water.

C � S � H þ SO4

ondary generated:

R-SR 0.

Figure 16.

145

(10,000� magnification).

mately the same, 38 MPa.

2 Na<sup>þ</sup> þ SO4

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3.7 Concrete based on steel slag as aggregate

<sup>2</sup>� ! CSH2 when a reaction proceeds in Na2SO4 solution (2)

The formed gypsum binds to tricalcium aluminate (C3A), in particular to ettringite, but also monosulphate (CaO)3(Al2O3)(CaSO4)12H2O(C4ASH12) is sec-

Fundamental Properties of Industrial Hybrid Cement Important for Application in Concrete

Ettringite formation is also accompanied by another minor reaction:

Reaction products of sulphate attack (gypsum and ettringite) are high-volume salts that cause destructive expansion of hydrated cement matrix. The tested H-Cement is specified by the major portion of the cement-less inorganic polymer (80% wt.) and the minor portion of the PC clinker (20% wt.). It contains a little C3A and when hydrated no Ca(OH)2. Therefore, just the composition of H-Cement is the cause of its high sulphate resistance because degradation processes, as described by Eqs. (1)–(5), cannot be applied with H-Cement use. Sulphate resistance of H-Cement is therefore regarded the same as sulphate-resistant CEM I 42.5

The temperatures and pressures in the testing laboratory autoclave were set according to the autoclave curves presented in Figure 17 in order to determine the volume changes of the concrete based on steel slag. The properties of the steel slag used for experimental research are shown in Tables 16 and 17. Figure 18 shows a gradual increase in the cube strength of concretes based on H-Cement and steel slag (HC concrete) as the aggregate compared with that consisting of PC with steel slag (PC concrete). HC concrete reports a smaller increase in strength, which equals that of PC concrete after 90 days of exposure in water. The characteristic concrete strength after 90 days in the case of the HC concrete and PC concrete is approxi-

The gradual increase in the cube strength of concretes based on H-Cement is caused by the fact that the hybrid cement generates lower hydration heat during the

SEM image of SR mortar (left) and HC mortar (right) after 5 years of exposure in sodium sulphate

<sup>2</sup>� <sup>þ</sup> Ca2<sup>þ</sup> <sup>þ</sup> aq: ! 2 Na<sup>þ</sup> <sup>þ</sup> CSH2 <sup>þ</sup> aq: (3)

C3A þ 3 CSH2 þ 26 H ! C6AS3H32 (4)

C4ASH12 þ 2 CSH2 þ 16 H ! C6AS3H32 (5)

#### Figure 14.

TG-DTA plots of HC mortar after 5 years in 5% wt. sodium sulphate and water.


Abbreviations: SSAP, specific surface area of total open pores; VTP, volume of total open pores (1.82–0.534 nm); MTP, total pore median radius; MMP, micropore median radius (1.82–5250 nm); TP, total open porosity (1.82–0.534 nm); K, permeability coefficient (calculated from the MIP results).

#### Table 15.

Basic pore structure parameters of PC mortar after 4-year immersion as well as SR and HC mortar after 5-year exposure in aggressive 5% Na2SO4.

Figure 15.

Destroyed integrity of PC mortar after 4 years of aggressive attack with sodium sulphate (left) and intact state of H-cement after 5 years of aggressive attack of 5% wt. Na2SO4 (right).

#### 3.6 Explanation of sulphate resistance of hybrid cement

Degradation of the hydrate phase of cement-based composite by sulphate attack is characterized by the formation of gypsum CaSO4.H2O(CSH2) together with ettringite (CaO)3(Al2O3)(CaSO4)3.32H2O(C6AS3H32). Gypsum is formed by the reaction of sulphate ions with Ca(OH)2 or calcium silicate hydrate (C-S-H):

$$\text{C} \, \text{OH} - + \text{SO}\_4{}^{2-} + \text{Ca}^{2+} \rightarrow \text{CSH}\_2 \, \text{or} \tag{1}$$

Fundamental Properties of Industrial Hybrid Cement Important for Application in Concrete DOI: http://dx.doi.org/10.5772/intechopen.88060

$$\text{C}-\text{S}-\text{H} + \text{SO}\_4^{2-} \rightarrow \text{CSH}\_2 \text{ when a reaction proceeds in Na}\_2\text{SO}\_4 \text{ solution} \quad \text{(2)}$$

$$2\text{ Na}^+ + \text{SO}\_4^{2-} + \text{Ca}^{2+} + \text{aq.} \rightarrow 2\text{ Na}^+ + \text{GSH}\_2 + \text{aq.} \tag{3}$$

The formed gypsum binds to tricalcium aluminate (C3A), in particular to ettringite, but also monosulphate (CaO)3(Al2O3)(CaSO4)12H2O(C4ASH12) is secondary generated:

$$\text{C}\_3\text{A} + \text{3 CSH}\_2 + 2\text{6 H} \rightarrow \text{C}\_6\text{AS}\_3\text{H}\_{32} \tag{4}$$

Ettringite formation is also accompanied by another minor reaction:

$$\text{C}\_4\text{ASH}\_{12} + 2\text{ CSH}\_2 + 16\text{ H} \rightarrow \text{C}\_6\text{AS}\_3\text{H}\_{32} \tag{5}$$

Reaction products of sulphate attack (gypsum and ettringite) are high-volume salts that cause destructive expansion of hydrated cement matrix. The tested H-Cement is specified by the major portion of the cement-less inorganic polymer (80% wt.) and the minor portion of the PC clinker (20% wt.). It contains a little C3A and when hydrated no Ca(OH)2. Therefore, just the composition of H-Cement is the cause of its high sulphate resistance because degradation processes, as described by Eqs. (1)–(5), cannot be applied with H-Cement use. Sulphate resistance of H-Cement is therefore regarded the same as sulphate-resistant CEM I 42.5 R-SR 0.

#### 3.7 Concrete based on steel slag as aggregate

The temperatures and pressures in the testing laboratory autoclave were set according to the autoclave curves presented in Figure 17 in order to determine the volume changes of the concrete based on steel slag. The properties of the steel slag used for experimental research are shown in Tables 16 and 17. Figure 18 shows a gradual increase in the cube strength of concretes based on H-Cement and steel slag (HC concrete) as the aggregate compared with that consisting of PC with steel slag (PC concrete). HC concrete reports a smaller increase in strength, which equals that of PC concrete after 90 days of exposure in water. The characteristic concrete strength after 90 days in the case of the HC concrete and PC concrete is approximately the same, 38 MPa.

The gradual increase in the cube strength of concretes based on H-Cement is caused by the fact that the hybrid cement generates lower hydration heat during the

#### Figure 16.

SEM image of SR mortar (left) and HC mortar (right) after 5 years of exposure in sodium sulphate (10,000� magnification).

3.6 Explanation of sulphate resistance of hybrid cement

H-cement after 5 years of aggressive attack of 5% wt. Na2SO4 (right).

Mortar SSAP (m2

Compressive Strength of Concrete

5-year exposure in aggressive 5% Na2SO4.

Table 15.

Figure 14.

Figure 15.

144

/g) VTP (cm<sup>3</sup>

TG-DTA plots of HC mortar after 5 years in 5% wt. sodium sulphate and water.

(1.82–0.534 nm); K, permeability coefficient (calculated from the MIP results).

2 OH � þSO4

Degradation of the hydrate phase of cement-based composite by sulphate attack

Destroyed integrity of PC mortar after 4 years of aggressive attack with sodium sulphate (left) and intact state of

<sup>2</sup>� <sup>þ</sup> Ca2<sup>þ</sup> ! CSH2 or (1)

/g) MTP (nm) MMP (nm) TP (%) K (m/s)

PC 5.32 0.100 252.00 84.65 19.39 3.3 � <sup>10</sup>�<sup>10</sup> SR 2.90 0.55 55.40 28.51 11.95 2.2 � <sup>10</sup>�<sup>12</sup> HC 11.17 0.100 31.46 19.91 19.67 8.0 � <sup>10</sup>�<sup>11</sup> Abbreviations: SSAP, specific surface area of total open pores; VTP, volume of total open pores (1.82–0.534 nm); MTP, total pore median radius; MMP, micropore median radius (1.82–5250 nm); TP, total open porosity

Basic pore structure parameters of PC mortar after 4-year immersion as well as SR and HC mortar after

is characterized by the formation of gypsum CaSO4.H2O(CSH2) together with ettringite (CaO)3(Al2O3)(CaSO4)3.32H2O(C6AS3H32). Gypsum is formed by the reaction of sulphate ions with Ca(OH)2 or calcium silicate hydrate (C-S-H):

• After 28 days, HC concrete shows a lower strength by 1.2 MPa (4.1%).

Fundamental Properties of Industrial Hybrid Cement Important for Application in Concrete

• After 28 days, PC concrete shows a lower strength by 5.4 MPa (15.6%).

• After 90 days, HC concrete shows a lower strength by 5.0 MPa (13.0%).

• After 90 days, PC concrete shows a lower strength by 6.5 MPa (17.1%).

• The difference in prism strength of PC concrete is 0.9 MPa (2.8%).

• The difference between the prism strength of HC concrete is 4 MPa (13.8%).

The results of durability tests of the concrete based on steel slag showed the suitability of H-Cement as a binder for the production of the concrete based on steel slag in an environment with a higher temperature and pressure. The above-stated fact is well-confirmed by Figure 19, where the comparison of test specimens after the autoclaving process is shown. The PC concrete with steel slag as aggregate was disintegrated into rubbles, while that composed of H-Cement remained compact and without any apparent damage. The autoclaving process (see Figure 17) of concrete containing steel slag and CEM I (PC concrete) resulted in a disruption of the cement compound due to shrinkage with increasing temperature. The autoclaving process accelerated the calcium disintegration and the magnesium disintegration of steel slag, which is associated with volume changes. This process has caused the disintegration of the test specimens. The autoclaving process of concrete

It is therefore evident that:

DOI: http://dx.doi.org/10.5772/intechopen.88060

Figure 18.

Table 18.

147

Average values of cube strengths from the first stage of the experiment.

Age of concrete HC concrete (MPa) PC concrete (MPa)

Cube 28 days 29.1 27.9 34.6 29.2 Cube 90 days 38.4 33.4 38.0 31.5 Prism 28 days 29.0 25.0 31.2 32.1

Comparison of cube and prism strengths after 28 and 90 days from the first and second stage of the experiment.

First stage Second stage First stage Second stage

Figure 17. Temperature-pressure conditions and concrete autoclaving time.


Table 16.

Values of bulk density and absorption power of steel slag with the fraction of 0/8 mm.


#### Table 17. Results of chemical analysis of steel slag.

initial hydration and thus makes it possible to reduce the volume changes during setting and hardening of the concrete mixture based on steel slag.

Table 18 compares the average values of cube strengths after 28 and 90 days and prism strengths after 28 days from the first and second stages of the experiment.

When comparing the results of the cube strength from the first and second stage of the experiment, the next partial observations may be drawn:

Fundamental Properties of Industrial Hybrid Cement Important for Application in Concrete DOI: http://dx.doi.org/10.5772/intechopen.88060


It is therefore evident that:


The results of durability tests of the concrete based on steel slag showed the suitability of H-Cement as a binder for the production of the concrete based on steel slag in an environment with a higher temperature and pressure. The above-stated fact is well-confirmed by Figure 19, where the comparison of test specimens after the autoclaving process is shown. The PC concrete with steel slag as aggregate was disintegrated into rubbles, while that composed of H-Cement remained compact and without any apparent damage. The autoclaving process (see Figure 17) of concrete containing steel slag and CEM I (PC concrete) resulted in a disruption of the cement compound due to shrinkage with increasing temperature. The autoclaving process accelerated the calcium disintegration and the magnesium disintegration of steel slag, which is associated with volume changes. This process has caused the disintegration of the test specimens. The autoclaving process of concrete


Average values of cube strengths from the first stage of the experiment.


#### Table 18.

Comparison of cube and prism strengths after 28 and 90 days from the first and second stage of the experiment.

initial hydration and thus makes it possible to reduce the volume changes during

Bulk density of grains 3.742 Mg m<sup>3</sup> Bulk density of grains after drying in a dryer 3.439 Mg m<sup>3</sup> Bulk density of grains saturated with water and surface dried 3.520 Mg m<sup>3</sup> WA24 water absorption 2.34%

Constituent Unit Result Uncertainty Element Unit Result Na2O % wt. 0.46 0.10 V mg/kg 570 MgO % wt. 10.2 1.2 Cr mg/kg 3900 Al2O3 % wt. 2.43 0.27 Ni mg/kg 25 SiO2 % wt. 13.7 1.3 Cu mg/kg 38 P2O5 % wt. 0.91 0.09 Zn mg/kg 63 SO3 % wt. 0.50 0.06 Sr mg/kg 130 K2O % wt. <0.003 Zr mg/kg 140 CaO % wt. 38 2 Nb mg/kg 67 TiO2 % wt. 0.29 0.02 Mo mg/kg 36 MnO % wt. 3.02 0.13 Ba mg/kg 200 Fe total % wt. 22 Ta mg/kg 110 CaO free % wt. 2.34 0.24 W mg/kg 86 — —— — Loss by annealing % wt. 0.74

Values of bulk density and absorption power of steel slag with the fraction of 0/8 mm.

Table 18 compares the average values of cube strengths after 28 and 90 days and prism strengths after 28 days from the first and second stages of the experiment. When comparing the results of the cube strength from the first and second stage

setting and hardening of the concrete mixture based on steel slag.

Figure 17.

Compressive Strength of Concrete

Table 16.

Table 17.

146

Results of chemical analysis of steel slag.

Temperature-pressure conditions and concrete autoclaving time.

of the experiment, the next partial observations may be drawn:

Acknowledgements

DOI: http://dx.doi.org/10.5772/intechopen.88060

Conflict of interest

Author details

\*, Pavel Martauz<sup>2</sup>

1 Building Testing and Research Institute, Bratislava, Slovakia

3 Faculty of Mining and Geology, VŠB-Technical University of Ostrava, Ostrava,

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

2 Považská Cementáreň Cement Plant, Ladce, Slovakia

\*Address all correspondence to: janotka@tsus.sk

provided the original work is properly cited.

Ivan Janotka<sup>1</sup>

Czech Republic

149

The financial support of this research project based on the contract related to the utility properties and durability of developed new cement kinds by the Považská

Fundamental Properties of Industrial Hybrid Cement Important for Application in Concrete

, Michal Bačuvčík1 and Vojtĕch Václavík3

cementáreň, a. s., cement plant, Ladce (Slovakia), is greatly appreciated.

The authors do not register any conflict of interest.

Figure 19. View on (a) HC concrete and (b) PC concrete after autoclaving.

containing steel slag and H-Cement (HC concrete) has eliminated the volume changes of the steel slag (calcium and magnesium expansion). There was no disruption of the cement compound and the contact zones between the grain of steel slag and the cement compound. This is confirmed by an increase in the concrete strength after the autoclaving process from 29.1 to 43.0 MPa (increase by 32%).
