WO2024105460A1

WO2024105460A1 - An eco-friendly calcium aluminate cement mixed with zeolite and pumice

Info

Publication number: WO2024105460A1
Application number: PCT/IB2023/056961
Authority: WO
Inventors: Alireza RASEKHISAHNEH; Ayli KALTEHEI; Seyedhessam MADANI; Jamshid ROSTAMI; Eilia RASEKHISAHNEH
Original assignee: Rasekhisahneh Alireza; Kaltehei Ayli; Madani Seyedhessam; Rostami Jamshid; Rasekhisahneh Eilia
Priority date: 2023-07-05
Filing date: 2023-07-05
Publication date: 2024-05-23

Abstract

This invention is about the effect of pumice and zeolite on the mechanical, microstructural, and durability properties of CAC composites. the solution is to add some special materials instead of a percentage of cement, which causes a secondary reaction called Stratlingite, as a result of which the stable phase C-A-S-H is formed instead of the non-stable phases CAH10 and C2AH8 and reduces the effect of the transformation phenomenon and improves the properties of cement. Also, by adding pumice and zeolite, it has reduced the conversion phenomenon and significantly improved the CAC properties, and it has reduced the cost and environmental pollutants.

Description

An eco-friendly calcium aluminate cement mixed with zeolite and pumice

This invention is about the effect of pumice and zeolite on the mechanical, microstructural, and durability properties of CAC composites. the solution is to add some special materials instead of a percentage of cement, which causes a secondary reaction called Stratlingite, as a result of which the stable phase C-A-S-H is formed instead of the non-stable phases and and reduces the effect of the transformation phenomenon and improves the properties of cement. Also, by adding pumice and zeolite, it has reduced the conversion phenomenon and significantly improved the CAC properties, and it has reduced the cost and environmental pollutants.

B01F 101/28 - C04B 28/06 - C04B 35/66

System and method for making and applying a non-Portland cement-based material

United States Patent 11351698

A system and method for applying a construction material is provided. The system may include a batching and mixing device configured to mix blast furnace slag material, geopolymer material, alkali-based powder, and sand to generate a non-Portland cement-based material, the non-Portland cement-based material including 4% to 45% geopolymer material by weight; greater than 0% to 40% blast furnace slag material by weight, 10% to 45% alkali by weight, 20% to 90% sand by weight, less than 1% sulfate by weight, and/or no more than 5% calcium oxide by weight; a conduit configured to transport the non-Portland cement-based material from the batching and mixing device; and a nozzle configured to receive the non-Portland cement-based material and combine the transported non-Portland cement-based material with liquid to generate a partially liquefied non-Portland cement-based material, wherein the nozzle is further configured to pneumatically apply the partially liquefied non-Portland cement-based material to a surface.

High early strength pozzolan cement blends

United States Patent 8323399

A high early strength blended cement composition includes larger sized fly ash and/or natural pozzolan particles blended with smaller sized hydraulic cement particles containing tricalcium silicate and/or dicalcium silicate (e.g., Portland cement and/or ground granulated blast furnace slag). Excess calcium released from the hydraulic cement particles when mixed with water forms calcium hydroxide available for reaction with the fly ash and/or natural pozzolan. The fineness of the hydraulic cement particles is substantially greater than the fineness of the fly ash and/or natural pozzolan particles (e.g., about 1.25 to about 50 times greater). Reducing or eliminating coarse hydraulic cement particles that cannot fully hydrate but include unreacted cores reduces or eliminates wasted cement normally found in concrete. Replacing some or all of the coarse cement particles with coarse pozzolan particles provides a blended cement composition having significantly lower water demand compared to the hydraulic cement fraction by itself.

Sialite binary wet cement, its production method and usage method

United States Patent 7708825

The technical field of the invention belongs to concrete and cement. The invention relates to a sialite binary wet cement and its package, transportation, storage and application. The sialite binary wet cement is composed of a “female body” as a primary component and a “male body” as a secondary component both of which are produced, stored, and transported separately, and are mixed together when they are used, wherein the “female body” and the “male body” each have a specific surface area of 2800-7500 cm2/g, the “female body” is mainly composed of inorganic cementitious materials and water, and it is in slurry, paste or wet powder form during the whole period of its production, storage, transportation and usage; the “male body” is mainly composed of inorganic cementitious materials, and it can be a wet form or a dry powder form. When they are used, the “female body” and the “male body” are mixed together with a small amount of regulating agents. There is no generation of dust, SO2, NOx and CO2 during production and application of the sialite binary wet cement. Therefore, heavy pollution of a traditional cement industry is avoided, and energy consumption and cost of product are decreased. The starting materials of the said cement mainly come from natural mineral, various slag and cinder. The said cement can be used for building, traffic, water conservancy, mine filling, timbering, and solidation of roadbed.

Complex admixture and method of cement based materials production

United States Patent 6645289

The present invention relates to admixtures production and to a method of application of the admixtures in cement and concrete technology. The method allows production of high-strength and high durable cement based systems, as well as cement systems with specially designed properties of cheap high-volume mineral admixture cements.

System and method for making and applying a non-Portland cement-based material

United States Patent 11224894

A system and method for applying a construction material is provided. The method may include mixing blast furnace slag material, geopolymer material, alkali-based powder, and sand at a batching and mixing device to generate a non-Portland cement-based material. The method may also include transporting the non-Portland cement-based material from the mixing device, through a conduit to a nozzle and combining the transported non-Portland cement-based material with liquid at the nozzle to generate a partially liquefied non-Portland cement-based material. The method may further include pneumatically applying the partially liquefied non-Portland cement-based material to a surface.

COMPLEX ADMIXTURE AND METHOD OF CEMENT BASED MATERIALS PRODUCTION

United States Patent Application 20030188669

The present invention relates to admixtures production and to a method of application of the admixtures in cement and concrete technology. The method allows production of high-strength and high durable cement based systems, as well as cement systems with specially designed properties or cheap high-volume mineral admixture cements.

The current invention aims at the influence of pumice and zeolite as supplementary cementations’ materials (SCMs) on the characteristics of calcium aluminate cement (CAC) composites. For this purpose, SCMs were used in substitution levels of 5%, 15%, 25%, 40%, and 60% of CAC. The results indicate that the active SCMs greatly influenced enhancing the cement composites' characteristics. For instance, the mixtures with 40% pumice and zeolite outperformed the plain mixture in the compressive strength test by about 45% and 90% at 90 days, respectively. At the age of 90 days, the rapid chloride migration coefficient for the optimal mixture of Z40 (containing 40% zeolite) was reduced by about 93%, and the electrical resistance was increased by about 70% in comparison to the age of 28 days; however, at the same ages, for the plain mixture, the rapid chloride migration coefficient was increased by about 74%, and the electrical resistance was decreased by about 60%. At the age of 90 days, the electrical resistivity of the Z40 mixture was 685% higher compared to the plain mixture. The results show that the high cost of CAC composite could be significantly lowered by utilizing SCMs. Moreover, it must be mentioned that the effect of high dosages of pumice and zeolite on the durability properties of this type of cement has not been studied previously, which can be considered an innovation of this invention.

Calcium aluminate cements (CAC) are classified as hydraulic cements and are mostly used in applications involving extreme environments, which include refractories, acid-resistant requirements, and fast-setting cements. These materials are currently the subject of research on topics like property improvement, durability and more friendly manufacturing processes. Calcium aluminate cement is a special cement with unique characteristics, however, the decrease in strength and durability because of the occurrence of the transformation phenomenon has severely limited the wide application of this cement and it has made it impossible to take full advantage of its good benefits. The conversion process increases the porosity and as a result, reduces the strength and durability of concrete. Monocalcium aluminate (CA) is the most important unhydrated phase in this cement. Monocalcium aluminate hydrates to form 4 main phases and . These hydrated products are divided into two main groups. The non-stable group that includes and the stable group that includes and phases. During the transformation process, non-stable phases become stable and leave their consequences. The transformation process is one of the inherent characteristics of calcium aluminate cement and its occurrence is thermodynamically unavoidable in this cement. Due to this decrease in resistance; It is necessary to calculate the concrete containing calcium aluminate cement based on the strength after conversion, but the estimation of the reduced strength seems to be impossible, so in many cases, engineers ignore the undeniable advantages of this cement and leave it aside. The second problem of calcium aluminate cement is its high price compared to Portland cement, and the reason for the high cost is due to the limited resources of bauxite soil, which is the main source of aluminum in the production of aluminate cement.

The above-mentioned problems need a suitable answer so that this cement can be used more widely, like Portland cement and take maximum advantage of its unique advantages. The proposed solution is to add some special materials instead of a percentage of cement, which causes a secondary reaction called Stratlingite, as a result of which the stable phase C-A-S-H is formed instead of the non-stable phases and and reduces the effect of the transformation phenomenon.

Solution of problem

Calcium aluminate cement (CAC) is an appropriate binder in the construction industry owing to its high abrasion resistance, high acid resistance, and high strength. CAC concrete can be poured into a place like Portland cement and converted from liquid to solid at room temperature. Furthermore, unlike the production of Portland cement, CAC production leads to lower emissions, which can be so beneficial regarding the environmental aspect. CAC concretes are utilized in broad applications such as the refractory and building industry.

There are two main reasons for restricting the use of CAC cement; first, the hydration process in CAC cement is entirely different from that of Portland cement. During the hydration process of CAC cement, stable phases such as: (gibbsite) and , metastable phases, such as and , or a combination of these two phases can be produced. As expressed in Equations and , the metastable phases are gradually converted into stable phases over time, known as conversion processes. As a result, the porosity is increased, and the compressive strength is reduced.

Secondly, the cost of CAC production is higher than Portland cement due to the bauxite supply limitation. To make CAC cement a reliable alternative to Portland cement, these two challenges should be addressed. Several studies have proposed different methods to suppress the conversion process, one of which is curing CAC concrete at high temperatures. The researches show that the stable phases ( and ) are formed at temperatures of 40–60 Centigrade, while the phase is formed at temperatures below 20 Centigrade. Other studies also reported that and phases are formed at temperatures of 20–40 Centigrade.

In recent years, supplementary cementations’ materials (SCMs) have been widely used in the construction industry due to the capability of these materials to produce durable concrete with lower emissions. A significant benefit of using SCMs is attributed to the environmental aspect of concrete production. Each year, large amounts of waste materials such as industrial wastes, and dust are disposed of in the environment, which could be hindered by using these materials as SCMs in concrete. The hydration mechanism of the CAC-SCMs composite may be changed by the incorporation of SCMs. For instance, using SCMs such as ground granulated blast furnace slags may form the stratlingite ( ) phase believing to mitigate the conversion process due to the high stability of this phase. Kırca et al. reported that the high-level incorporation of ground-granulated blast furnace slags (more than 40%) in CAC composite could limit the conversion process without generating strength loss. In another study, Collepardi et al stated that incorporating 15% silica fume could reduce the strength loss because of the formation of stratlingite, which could mitigate the conversion of metastable phases.

As stated previously, the conversion process as an essential factor affecting the performance of the CAC cement needs to be studied; therefore, the main purpose of the present research is to study the effect of adding pumice and zeolite as SCMs on the conversion process. As the conversion process cannot be directly tested, the effect of the conversion process on the mechanical and durability properties has been evaluated. More specifically, pumice and zeolite are used as supplementary cementations’ materials in substitution levels of 5%, 15%, 25%, 40 %, and 60%. During the current research, the compressive strength, modulus of rupture, modulus of elasticity, rapid chloride migration, electrical resistivity, permeable pore space, XRD, and microstructural analyses were performed to study the mechanical and durability properties. Additionally, a simple cost and environmental analysis were also carried out.

A lot of studies have investigated binary and ternary Portland cement, however, binary and ternary calcium aluminate cement composites have rarely been studied. In particular, the effect of pumice and zeolite on the durability of this type of cement has not been studied, which can be considered as an innovation of this study. The results can also be applicable in developing standards for calcium-aluminate cement.

This invention is about the effect of pumice and zeolite on the mechanical, microstructural, and durability properties of CAC composites. For this purpose, 11 mixtures with different substitution levels of SCMs were prepared and evaluated. The most significant achievements of the present invention can be summarized as:

The plain mixture reaches the compressive strength of 44 MPa at the age of 28 days; however, by increasing the age to 90 days, the compressive strength of the plain mixture was reduced to 24 MPa due to the occurrence of the conversion phenomenon. In addition, the modulus of rupture and electrical resistivity of the plain mixture decreased respectively by 16% and 60%. Meanwhile, the permeable pore space and the RCMT coefficient were increased by 28% and 74%.
The results showed that, in contrast to the plain mixture, the durability and mechanical properties of the CAC mixtures containing zeolite and pumice were enhanced. At the age of 90 days compressive strength, modulus of rupture, permeable pore space, electrical resistance, and RCMT coefficient for the P40 mixture were improved by 46%,152%,15%,246%, and 92%, respectively compared to the age 28 days, and for the Z40 mixture were enhanced by 9%,141%,18%,70%, and 94% respectively. This improvement may be because of the formation of the stable stratlingite phases and the mitigating effect of pumice and zeolite on the conversion processes. Moreover, it is noteworthy to mention that even mixes containing 60% zeolite and pumice can be used in structural concrete.
Microstructural analysis reveals that the P40 and Z40 mixtures have a homogeneous and densified microstructure compared to the plain mixture, showing that pumice and zeolite incorporation could limit the conversion process and can improve the microstructure of the CAC composite. XRD analysis demonstrated that pumice and zeolite were capable of reducing conversion processes.

Advantage effects of invention

After using specific mineral materials in the optimal percentage, the mechanical properties and durability of the mixtures were investigated. The results showed that as the age of the control sample (containing only cement and without substitute materials) increased due to the occurrence of the transformation phenomenon, it experienced a drop in mechanical characteristics and durability, but at the same age, the characteristics of the samples containing substitute materials experienced significant improvement. For example, at the age of 90 days compared to 28 days in the control sample, the compressive strength decreased by 45%, the electrical resistance decreased by 60%, and the chloride ion migration coefficient increased by 74%, while at the same age, for optimal mixtures containing substitute materials compressive strength increased by 47% and 90%, electrical resistance increased by 400% and 685%, and the accelerated migration coefficient of chloride ion, which is a very important measure of concrete permeability, decreased by 78% and 85%. In addition, it was determined that the use of the mentioned materials it reduced the total cost by 30% and greenhouse gas emissions by 35%.

SEM images of plain, Z40 and P40 mixture at the age of 28 days

SEM images of plain, Z40 and P40 mixture at the age of 90 days

Examples

Materials properties

Calcium aluminate cement (manufactured by Kerneos Inc, France) was used in the mixtures. The chemical composition of the CAC is shown in Table 1. In this paper, natural sand was used as aggregate. In Tables 2 and 3, the properties of the natural sand are included. A polycarboxylate ether-based superplasticizer with a specific gravity of 1.1 g/cm3 was used in this paper. The pumice and zeolite were utilized as the SCMs. The chemical and physical properties of SCMs are provided in Table 1.

[Table. 1] Physical properties and chemical composition of the cement, pumice and zeolite

Properties									Specific gravity ) g.cm^-3	BET Surface area (cm².g^-1)	LOI

CAC	4.25	10.14	43.45	40.3	0.61	0.05	0.09	0.1	3.24	3600	0.55
P	61	5	19	8	2.1	0.4	1.6	2	2.63	4500	0.9
Z	67.1	1.46	13.9	7.04	3.15	0.05	1.62	1.19	2.25	6800	2.1

[Table. 2] Properties of the natural sand

Properties	maximum nominal size(mm)	SSD Density (kg.m^-3	SSD water absorption (%)
Natural sand	4.75	2640	2.03

SSD: Saturated Surface Dry

[Table. 3] Size gradation of the sand used in this study

Sieve number	4	8	16	30	50	100	200
Cumulative percent passing	71.5	44.4	29.8	14.2	6.1	1.5	1.28

Mix design and specimen’s preparation:

The mixtures were prepared at water to cementations’ ratio of 0.4. The cement content was kept constant at a level of 550 kg/m3. High cost is a challenge of using calcium aluminate cement that needs to be addressed. In this regard, researchers have studied the effect of replacement at different levels (low to high). Available research shows that other studies have investigated the replacement level in the range of 15%-40%. In this study, SCMs were considered as a portion of cement in levels of 5%, 15%, 25%, 40%, and 60% by weight of cement. In the following notes, the method of preparing mixtures is provided:

Dry ingredients were mixed for 1.5 min.
Adding water to the dry ingredients.
Mixing the cement composite for 2 min and adding the required superplasticizer.
Continuing mixing for another 4 min.
Mix proportions are shown in Table 4. It is worth mentioning that after casting, for minimizing water evaporation, all specimens were protected with a plastic sheet for 24 hours. After that, the samples were demoded and cured in water at a temperature of 22 ± 2 °C.

[Table. 4] The mortar mixture proportions

Mix	CAC (kg.m^-3)	Sand (SSD) (kg.m^-3)	SCMs (kg.m^-3)	Water (kg.m^-3)	Superplasticizer (kg.m^-3)	Flowability (cm)
Plain	550	1523	-	220	0	19.5
P5	522.5	1495.8	27.5	220	0.97	19.2
P15	467.5	1485.7	82.5	220	1.76	20
P25	412.5	1475.8	137.5	220	2.7	19.7
P40	330	1460.9	220	220	3.6	20
P60	220	1441.1	330	220	5	19.5
Z5	522.5	1491.2	27.5	220	1.2	18.5
Z15	467.5	1472.4	82.5	220	2.1	18.3
Z25	412.5	1453.5	137.5	220	4.68	18.7
Z40	330	1425.3	220	220	8.53	18.3
Z60	220	1387.6	330	220	17.95	19.1

Test methods:

Flowability

The flowability test results were determined in accordance with ASTM C1437. In this paper, the desired flowability was considered in the range of 19±1cm.

Compressive strength

Compressive strength test results were carried out, according to BS EN12390-3. At each age, four cubic specimens with the dimension of 50mm were tested.

Rapid Chloride Migration Test (RCMT)

RCMT was conducted in accordance with the NT BUILD492. After performing the test procedure according to the standard mentioned above, chloride ions penetration depth into the specimen covered with 0.1 M silver nitrate solution was measured by caliper. Then, the RCMT coefficient can be obtained using Eq:

: RCMT coefficient,

U: Voltage, V

T: Average temperatures in the anolyte solution at the initial and final stage, °C

L: Thickness of specimen, mm

X_d: Penetration depths, mm

t: Test duration, hour

Electrical resistivity

The Wenner method (four-point method), which is the most common method for measuring the electrical resistivity of cement composites, was employed to obtain the electrical resistivity of specimens. 100×200 mm cylindrical specimens were used for this test. The Wenner apparatus has four surface electrodes located at equal distances from each other. To calculate the electrical resistance, the Wenner device is attached to the concrete sample's surface, and an electric current is conducted between the electrodes. Then, the electrical resistivity was obtained using Eq.

ρ=2·π·a·

I: Electric current (A)

a: Distance between electrodes (cm)

ΔV: Potential difference (V)

ρ: Electrical resistivity (kΩ.cm)

Modulus of Rupture

The modulus of rupture test was measured in accordance with the BS-EN 196-1. In each age, three prismatic specimens were used. As required by the standard, the three-point loading method with a loading rate of 50 ± 10 N/s was used. The modulus of rupture was calculated according to Eq.

: Modulus of rupture, MPa

b: The width of the specimen, mm

: Load at the middle point, N

L: Supports distance, mm.

Modulus of elasticity

ASTM C469 was used to measure the modulus of elasticity. To remove any surface irregularity and make sure that both ends of the specimens are perpendicular to the sides of the specimen, both ends were ground. The loading rate of 0.28 MPa/s was applied during the test. Strain-measuring equipment attached to two fixed rings was used for measuring deformation. The static elastic modulus of concrete was measured in accordance with Eq.

E: Chord modulus of elasticity

: Stress at 40 % of the ultimate load

: Stress at a longitudinal strain of 50 millionths

: Longitudinal strain caused by

Permeable voids

At 28 days of age, the ASTM C642 [37] method was used to determine the permeable voids content. The following process is specified according to the standard for determining the permeable voids. Cylindrical specimens with a diameter of 100mm and a height of 50mm were dried at 105°C until they reach a constant weight. Afterwards, the dried specimens were immersed in water until they reach a constant weight. Using the following equation, the permeable voids content can be determined.

Permeable voids (%) =

=
=

A: the mass of dried sample (g),

C: the mass of the surface-dry sample after immersion and boiling (g),

D: apparent mass of sample in water after immersion and boiling (g),

ρ: density of water (g/cm³),

: the dry bulk density(g/cm³),

: the apparent density(g/cm³).

Scanning electron microscopy (SEM)

SEM was employed to study the effect of SCMs as supplementary cementations’ materials on the microstructure of mixtures in more details. TESCAN VEGA3 SEM apparatus was utilized to capture SEM images.

Economic and environmental assessment

Each mixture's cost and carbon footprint are estimated by adding up the prices and carbon footprints of its constituent parts. Eq.10 was used to compute the unit cost of each mixture.

M: Unit cost of a mixture per cubic meter.

: Unit cost of the i-th ingredient (i = 1, 2, 3, …, n).

: Mass of the i-th ingredient of the mixture.

Eq. 11 was used to determine the carbon footprint of each mixture:

Where global warming index is the carbon footprint of a mixture per cubic meter;

: Unit carbon footprint of the i-th ingredient (i = 1, 2, 3… n).

: Mass of the i-th ingredient of the mixture.

The unit cost and carbon footprint of the materials used in the investigated mixes are shown in Table 5.

[Table. 5] Database used for unit cost and carbon footprint of raw materials.

Ingredients	Cost (USD/kg)	Carbon footprint (kg-CO₂/kg)
CAC	1.8	0.72
Sand	0.01	0.002
Pumice	0.05	0.004
Zeolite	0.053	0.03
SP	6	0.772
Water	0.005	0.001

Results and Discussion

XRD analysisAn X-ray diffraction experiment can reveal cement paste's crystalline structure [44]. Diffraction patterns for the investigated mixtures at 7 and 90 days of hydration are shown in . As it is clear, the metastable phases and are identified at the age of 7 days in the plain mixture. The presence of these phases is highly correlated with high strength at an early age [44]. However, at the later age of 90 days, the metastable phases are not detected in the plain mixture, indicating that the metastable phases have been converted to the stable ones. This may lead to the decrease in strength of the plain mixture at the age 90 days.At the age of 7 days, the XRD patterns for the mixtures containing zeolite and pumice show the presence of the metastable and stable phases. In addition, the presence of the stratlingite (→( phase is detectable in mixtures containing 40% pumice and zeolite at the age of 7 days, demonstrating the reactivity of pumice and zeolite at an early age. Furthermore, at this age, it is clear that the metastable phases are lower in mixtures containing pumice and zeolite than in the plain mixtures, indicating that these materials effectively decrease the production of the metastable phases. The amount of the stable phase of stratlingite is increased with the age of mixtures, which could explain why these materials have an appropriate performance in the CAC composites.

Table. 6 The X-ray diffraction patterns for the plain mixture and the mixtures containing 40 % SCMs after 7 and 90 days of hydration

The compressive strength

The results from 1 day up to 90 days are represented in Figures 2 to 3. It is clear from the figures that the CAC composites have high compressive strength at early ages. The plain mixture has a compressive strength of more than 33 MPa at the age of 1 day. By increasing the age up to 28 days, the plain mixture has shown an increasing trend, reaching 44.5 MPa. Nevertheless, unlike the Portland cement mixture, by increasing the age up to 90 days, the CAC cement composite has shown a decreasing trend owing to the conversion processes. For instance, the compressive strength of the plain mixture was decreased by 45%.

The obtained results show that incorporating pumice and zeolite especially at high replacement levels, results in lower strengths at an early age. Moreover, replacing pumice and zeolite up to 15% has not prevented the reduction in compressive strength at later age, therefore this percentage of replacement is not optimal and is not recommended. The stable phases and are the major reason for the long-term strength of calcium aluminate cement mixtures. During the hydration process at ambient temperature, the metastable phases of and are formed earlier than stable phases. These metastable phases have a large amount of water in their structure and also have a low density enabling these phases to fill the space originally occupied by water and give high early strengths. However, it should be mentioned that these early strengths, which may persist for several years are transient due to the occurrence of the conversion process, which is thermodynamically inevitable. The conversion process is responsible for the long-term strength reduction of CAC cement composite.

The current results indicate that the mixtures containing zeolite have superior performance among all mixtures at the age of 90 days. At the age of 90 days, the results reveal that increasing the replacement level of pumice and zeolite up to 40% could enhance the compressive strength, but beyond 40%, the compressive strength has shown a decreasing trend. In this study, the optimal replacement level is found to be 40%; however, the negative effects of the conversion process are mitigated in proportions above 25% for mixtures containing pumice and zeolite. Furthermore, at the age of 90 days by increasing the replacement level of pumice and zeolite up to 60%, the compressive strength has decreased, but it's noteworthy that these mixtures still have a higher compressive strength than the plain mixture which can be considered as a positive characteristic in sustainable development. Additionally, zeolite is more effective than pumice in obtaining higher compressive strength. For example, the Z40 mixture has 30% better performance in comparison to the P40 mixture. The higher specific surface area of zeolite compared to pumice could be the reason for the higher reactivity of zeolite compared to pumice.

As stated previously, by increasing the age of the mixtures to 90 days, the compressive strength of the plain mixture is 45% lower than that at the age of 28 days, however for the mixtures containing pumice, and zeolite an increasing trend is observed in comparison to the plain mixture. Table. 3 Indicates that the mixture containing 40% zeolite has superior performance among all the mixtures and, in comparison to the plain mixture, has 90% higher strength at the age of 90 days. Owing to the conversion process, porosity increases, and consequently, the strength decreases. In fact, during this process, the low-density metastable phases are changed to the stable phases with higher density. It should be mentioned that the strength loss for the plain mixture is significantly higher than the mixture Z5, Z15, and P5, which shows that incorporating pumice and zeolite can mitigate the strength loss owing to the reaction of the silica content of pumice and zeolite with calcium aluminate hydrates. A hexagonal hydrate of alumina and silica known as gehlenite or stratlingite has been proposed to form as a result of this reaction. This reaction could avoid the conversion of hexagonal to cubic.

Table. 2 Shows that at the age of 90 days the compressive strength is improved as the amount of pumice incorporation in cac is increased up to 40%. At the age of 90 days, the compressive strength improvement for the P25, P40, and P60 is 25%, 45%, and 40%, respectively, compared to the age of 28 days. Moreover, similar trend is observed for the zeolite mixtures.

[Table. 7]

Table. 7 Compressive strength of the pumice mixtures at the age of 1 to 90 days

[Table. 8]

Table. 8 Compressive strength of the zeolite mixtures at the age of 1 to 90 days

Modulus of rupture

In Tables 9 and 10, the modulus of rupture of mixtures is presented at the ages of 28 and 90 days. At the age of 28 days, the plain mixture has the maximum modulus of rupture among the mixtures. Additionally, it should be mentioned that the mixtures containing 5% and 15% pumice and zeolite have similar modulus of rupture to the plain mixture. However, by increasing the substitution level of pumice up to 60%, the Modulus of rupture decreases significantly, which clearly shows that pumice powder does not have a significant reaction at this stage.

By increasing the age of mixtures from 28 days to 90 days a different trend is observed. The plain mixture shows a significant reduction (16%) in modulus of rupture, which obviously shows that the conversion process has occurred at this age. Nevertheless, the mixtures containing pumice show an increasing trend in modulus of rupture. For instance, incorporation of 5%, 15%, 25%, 40% and 60% pumice increase the modulus of rupture by about 23%, 44%, 95%, 152% and 78% in comparison to the age of 28 days, respectively. This improvement may be because of the formation of the stable stratlingite phases and the mitigating effect of pumice on the conversion processes.

As is clear from table. 5, adding zeolite increases the modulus of rupture at the age of 90 days compared to the plain mixture. For instance, incorporation of 5%, 15%, 25%, 40% and 60% zeolite lead to 28%, 45%, 91%, 142% and 46% increases in modulus of rupture compared to the age of 28 days respectively. It is also observed that the Z40 mixture has the optimum performance in comparison to all mixtures. Increasing the replacement level of zeolite at the age of 28 days decreases the modulus of rupture showing that zeolite does not have high reactivity at this age. It is noteworthy to mention that, at the age of 90 days the mixtures containing 40% zeolite and pumice outperform the plain mixture by around 82% and 75% in modulus of rupture, respectively.

[Table. 9]

Table. 9. Modulus of rupture of the mixtures at the age of 28 days

[Table. 10]

Table. 10. Modulus of rupture of the mixtures at the age of 90 day

Modulus of elasticity

Table 10 shows the elastic modulus of mixtures at the age of 90 days. As it is clear, the incorporation of pumice and zeolite increases the elastic modulus of the mixtures compared to the plain mixture. For instance, the elastic modulus of mixtures containing 5%,15%, 25%, 40% and 60% pumice has increased by about 16%, 33%, 50%,79% and 8% respectively and for the mixtures containing 5%,15%, 25%, 40% and 60% zeolite has increased by about 50%, 54%, 71%, 96% and 10 % in comparison to the plain mixture, respectively. The mixture containing 40% zeolite has the best performance among all mixtures, which is compatible with the compressive and flexural strength results.

[Table. 11]

Table. 11 Modulus of elasticity of mixtures at the age of 90 days

Permeable voids

It is well known that the durability and mechanical properties of cement-based materials are highly influenced by the porosity. It should also be mentioned that the porosity in the cement matrix is dependent on the type of hydration products.

Table. 11 represents the permeable pore volume test results. As can be observed at the age of 28 days, incorporating the high content of pumice and zeolite has increased the permeable pore volume compared to the plain mixture. For instance, the incorporation of 5%, 15%, 25%, 40% and 60% pumice increases the permeable pore volume by about 11%, 17%, 16%, 5% and 25%, respectively. Furthermore, the incorporation of 5%, 15%, 25%, 40% and 60% zeolite increase the permeable pore volume by about 9%, 14%, 15%, 3% and 20% respectively. At the age of 28 days, the plain mixture has the lowest permeable pore space among all the mixtures, indicating a dense microstructure with lower porosity due to the formation of the metastable phases ( and). However, by increasing the age of mixtures from 28 days to 90 days, the plain mixture has an increasing trend (about 28%) in the volume of permeable pores showing that the conversion process has occurred. In the conversion process, the meta-stable phases with lower density are converted to the stable phases with higher density, which reduces the volume of solid, causing an increase in the porosity.

Despite the increased porosity in the plain mixture, the mixtures containing pumice and zeolite has a decreasing trend in the permeable pore volume. For example, the incorporation of 5%, 15%, 25%, 40%, and 60% pumice reduces by about 17%, 26%, 28%, 31%, and 25% of permeable pore volume compared to the plain mixture at the age of 90 days. In addition, the substitution of 5%, 15%, 25%, 40%, and 60% zeolite reduced approximately 21%, 31%, 33%, 35% and 27% of permeable pore space compared to the plain mixture at the age of 90 days. Thus, pumice and zeolite significantly influence suppressing and mitigating of the conversion process.

[Table. 12]

Table. 12 Permeable voids of the different mixtures at the age of 28 and 90 days

Rapid Chloride Migration Test (RCMT)

Regarding durability, a critical problem in the chloride environment is the corrosion of rebar in concrete. Therefore, it is highly beneficial to examine the permeability of concrete in chloride environments. It should be mentioned that the chloride permeability coefficients of CAC cement composites have not been seriously investigated in the previous studies.

Replacing Portland cement with SCMs may significantly reduce the concrete diffusivity against aggressive ions. However, this effect should also be comprehensively investigated in the CAC mixtures. As a matter of fact, SCMs affect the cement matrix via two main processes; they can act as a filler that seals the cement matrix as well as modify the characteristics and microstructure of the hydration product. The research reveals that silica-containing minerals such as fly ash, blast furnace slag, and silica fume are capable of improving the CAC composites.

The results of RCMT test are depicted in Table. 9 At the age of 28 days, the mixtures incorporating pumice and zeolite have a higher rapid chloride migration coefficient in comparison to the plain mixture. This phenomenon can be due to the non-occurrence of the conversion process and also the low reactivity of pumice and zeolite at this age.

As it can be observed in Table. 12, at the age of 90 days, the maximum RCMT coefficients are observed for the L60 mixture with a value of 12 and the mixture with 40% zeolite has the lowest RCMT coefficient, which is 0.9 . By increasing the age from 28 to 90 days, it is clear that the RCMT coefficient has been increased by 74% for the plain mixture, which shows the conversion process has occurred.

Using pumice mitigates the effect of the conversion process on the RCMT coefficient. For example, at the age of 90 days, the rapid chloride migration coefficients for the mixtures containing 5%,15%, 25%, 40%, and 60% pumice are 28%, 49%, 69%, 91%, and 86% lower compared to the age of 28 days, respectively. As well, the zeolite has a positive effect on mitigating the conversion process and reducing the RCMT coefficient of mixtures. For instance, the rapid chloride migration coefficient for the mixtures containing 5%, 15%, 25%, 40% and 60% zeolite shows 4%, 19%, 50%, 93% and 92% reduction compared to the age of 28 days, respectively. It should be mentioned that mixtures containing 40% of zeolite and pumice had 85% and 78% lower rapid chloride migration coefficients in comparison to the plain mixture at the age of 90 days. Mostafa et al. showed that adding SCMs can inhibit the conversion reaction. Similarly, Heikal et al. reported that adding slag to the CAC composite could inhibit the conversion process by forming stratlingite or gehlenite. As illustrated by Eqs.12 and 13, this is because the silica content of SCMs reacts with the main hydrate phases ( and) and forms the stable phase of stratlingite.

[Chem. 1] 2 + + + 9

[Chem. 2] +

As shown in Table. 12, at the age of 90 days incorporating pumice and zeolite reduced the RCMT coefficients owing to creating stratlingite phases instead of the metastable phases ( and ) and acting as filler, which could fill the gaps in the cement matrix.

[Table. 13]

Table. 13 Rapid Chloride Migration Test coefficient of the mixtures at the age of 28 days

Table. 13 Rapid Chloride Migration Test coefficient of the mixtures at the age of 90 days

Electrical resistivity

Electrical resistivity, which is a measure of the resistance of materials to the electrical current passage, has been considered as an index for investigating the durability of cement composites. Measuring electrical resistivity provides valuable information for evaluating the corrosion risk of reinforcement.

As it is clear from Figures 11 to 12, at the age of 1 day, the plain mixture has the highest electrical resistivity among the mixtures. However, at this age, the mixtures incorporating 5%, 15%, 25%, and 40% pumice and zeolite has almost a similar electrical resistivity to that of the plain mixture. This high electrical resistivity is due to the formation of the metastable phases, which should be considered transient due to the conversion process occurrence by time. By increasing the age of the samples to 28 days, the plain and P5 mixture's electrical resistivity values are increased due to the hydration of the cement. However, in the mixtures containing 15%, 25%, 40%, and 60% pumice, the electrical resistivity is decreased, which might be as a result of lower cement for hydration and low reactivity of pumice powder to create stratlingite phases. In the mixtures containing zeolite, a different trend is observed in comparison to the pumice mixtures. The results show that by increasing the age of the specimens up to 28 days, the mixtures containing 5%, 15%, and 25% zeolite have similar electrical resistivity to the plain mixtures, and Z40 by reaching 98 kΩ.cm electrical resistivity has a significant increase in comparison to the plain mixture indicating the high reactivity of zeolite compared to pumice.

The Research indicates that curing time has a major impact on the surface electrical resistivity by virtue of the progressive hydration of Portland cement. As can be seen in Table. 11, by increasing the age from 28 to 90 days, the electrical resistivity of the plain, P5, and P15 mixtures is reduced by about 60%, 55%, and 30%, respectively, which shows the significance of the conversion process. The occurrence of the conversion process increases the porosity of mixtures, which in turn can ease the flow of electrical current and reduce the electrical resistivity.

At the age of 90 days, the L5 mixture has the lowest electrical resistivity (16.4kΩ.cm), and the mixture with 40% zeolite (Z40) has the highest electrical resistivity (167.2kΩ.cm) among all the mixtures, which shows that zeolite has a significant effect on suppressing the conversion process. For instance, at the age of 90 days, the electrical resistivity values in the mixtures containing 25%, 40%, and 60% zeolite is improved by about 159%, 70%, and 73%, respectively, compared to the age of 28 days. Therefore, incorporating zeolite in a high replacement level improves the electrical resistivity and inhibits the occurrence of the conversion process. It is noteworthy to mention that the mixture containing 40% zeolite has about seven times the electrical resistance compared to the plain mixture at the age of 90 days.

It should be mentioned that using pumice also leads to improving the electrical resistivity. For example, in mixtures containing 25%, 40%, and 60% pumice, the electrical resistivity is enhanced by about 174%, 245%, and 200%, respectively.

The electrical resistivity can be categorized into four groups. The electrical resistivity less than 10 kΩ.cm is considered as a high-risk corrosion, the electrical resistivity between 10–50 kΩ.cm is considered as a moderate risk corrosion, and the electrical resistivity between 50–100 kΩ.cm is considered as low-risk corrosion. For the electrical resistivity, more than 100 kΩ.cm, the corrosion risk can be neglected. As it is clear from Figures 11 to 12, the plain mixture and the mixtures containing 5% and 15% pumice and zeolite can be categorized as the moderate risk of corrosion and the mixtures containing 25%, 60%, and 40% pumice and zeolite as the low and negligible risk of corrosion, respectively. Thus, using pumice and zeolite could notably improve the electrical resistivity of CAC composite and, accordingly, this durability index of CAC composite. It is worth mentioning that the result of electrical resistivity is compatible with other durability test results.

[Table. 14]

Table. 14.Electrical resistivity values of the pumice mixtures

[Table. 15]

Table. 15. Electrical resistivity values of the zeolite mixtures

SEM analysis

Figures 14 and 15 represent the scanning electron micrograph (SEM) of the mixtures. Table. 14. shows the microstructure of the mixtures at 28 days, which clearly indicates the densified cement matrix. This densified microstructure obviously shows that the conversion process has not been occurred significantly, which could be the reason for the high compressive strength of mixtures at this stage. Table. 15. indicates the SEM picture of the plain mixture at the age of 90 days. As can be seen in Fig. 15, due to the occurrence of the conversion process at this age, the microspores and micro-cracks are created in the plain and L40 mixtures, which could be a reason for the low mechanical and durability properties of these mixtures.

Generally, the strength is reduced as the porosity is increased in solids. The reason is that the solid part of the material resists external loads. Additionally, it is known that porosity affects durability properties. The higher the porosity, the weaker the investigated durability properties. Therefore, the increased porosity due to the conversion process can also explain the high permeability and low compressive strength of the plain and L40 mixtures at 90 days.

Table. 15. shows the SEM image of the mixture containing 40% pumice and zeolite. As it is demonstrated, the incorporation of 40% pumice and zeolite has improved the microstructure of the CAC composite. P40 and Z40 mixtures have a homogeneous and dense microstructure in comparison to the plain mixture. This can also support the higher compressive strength and improved durability properties of these mixtures. In Fig. 15, the stable phases are shown, and as is clear, the has a cubic structure while has a poorly crystalline structure and the stratlingite phases have a platy structure. These two phases are responsible for the long-term properties of the CAC composite. As stated earlier, SCMs with a high silica content can react with metastable phases and create the stratlingite phases (stable phase), which is shown in Table. 15. This reaction can inhibit and mitigate the conversion process. The microstructural analysis is in agreement with the obtained durability results.

Economic and environmental assessment

This section evaluates the investigated mixture's unit cost and carbon footprint. The unit cost and carbon footprint of the mixes are computed using the aforementioned inventory data, as shown in Figures 16 and 17 the plain mixture has the greatest overall cost as well as the largest quantity of GWP output in comparison to the other mixtures. As the SCMs replacement level increases, a downward trend is observed in the cost and quantity of GWP for all the mixtures.

As far as the environment is concerned, the results indicate that mixtures containing pumice outperformed mixtures containing zeolite. Moreover, the results show that using pumice and zeolite significantly decreases the GWP index of mixtures compared to the plain mixture. The results indicate that the plain mixture produced 400 kg.m^-3of carbon dioxide, while the mixture containing 60% zeolite and pumice produced about 186,167, and 171 kg.m³ of carbon dioxide. Additionally, the P40 and Z40 mixtures, which are the optimum mixtures in this study, lower GWP index by 38% and 36%, respectively.

A key parameter in CAC's preference for construction practices is the cost of production. As a result, the cost of CAC composite has a substantial impact on its usage potential. Furthermore, as the above results demonstrate, the addition of pumice and zeolite can significantly lower the cost of CAC composites. For instance, the usage of 60% pumice and zeolite has resulted in a 50% reduction in the overall cost in comparison to the plain mixture. As mentioned earlier, one of the critical drawbacks of CAC cement is its high cost. The findings indicated that by utilizing SCMs, this issue might be significantly alleviated.

[Table. 16]

Table. 16. The global warming index (GWI) of mixtures per cubic meter concrete

[Table. 17]

Table. 17 The total cost of mixtures per cubic meter concrete

In this invention, the structure of a special cement has been modified with specific minerals and a specific percentage and has improved the properties of cement. Including: compressive strength, Modulus of Rupture, modulus of elasticity, volumetric absorption, Permeable voids, Rapid Chloride Migration Test, electrical resistance, acid resistance, as well as XRD test and microstructure examination by electron microscope (SEM) in the laboratory. This new mixed cement can be easily used in structural applications with acceptable about strength and durability.

Claims

This invention is about the effect of pumice and zeolite on the mechanical, microstructural, and durability properties of CAC composites. For this purpose, 11 mixtures with different substitution levels of SCMs were prepared and evaluated and the solution is to add some special materials instead of a percentage of cement, which causes a secondary reaction called Stratlingite, as a result of which the stable phase C-A-S-H is formed instead of the non-stable phases and and reduces the effect of the transformation phenomenon. The durability and mechanical properties of the CAC mixtures containing zeolite and pumice were enhanced.
According to claim 1, the plain mixture reaches the compressive strength of 44 MPa at the age of 28 days; however, by increasing the age to 90 days, the compressive strength of the plain mixture was reduced to 24 MPa due to the occurrence of the conversion phenomenon.
According to claim 2, at the age of 90 days’ compressive strength for the P40 mixture were improved by 46% and for the Z40 mixture were enhanced by 9% compared to the age 28 days.
According to claim 1, the modulus of rupture and electrical resistivity of the plain mixture decreased respectively by 16% and 60%.
According to claim 4, at the age of 90 days’ modulus of rupture for the P40 mixture were improved by 152% and for the Z40 mixture were enhanced by 141% compared to the age 28 days.
According to claim 4, at the age of 90 days’ electrical resistance for the P40 mixture were improved by 246% and for the Z40 mixture were enhanced by 70% compared to the age 28 days.
According to claim 1, in the plain mixture, the permeable pore space and the RCMT coefficient were increased by 28% and 74%.
According to claim 7, at the age of 90 days’ permeable pore space for the P40 mixture were improved by 15% and for the Z40 mixture were enhanced by 18% compared to the age 28 days
According to claim 7, at the age of 90 days RCMT coefficient for the P40 mixture were improved by 92% and for the Z40 mixture were enhanced by 94% compared to the age 28 days
In this invention, the durability and mechanical properties of the CAC mixtures containing zeolite and pumice were enhanced which may be because of the formation of the stable stratlingite phases and the mitigating effect of pumice and zeolite on the conversion processes.
In this invention, the P40 and Z40 mixtures have a homogeneous and densified microstructure in comparison to the plain mixture, which that pumice and zeolite incorporation could limit the conversion process and improve the microstructure of the CAC composite.
XRD analysis demonstrated that pumice and zeolite were capable of reducing conversion processes.
In this invention, by adding pumice and zeolite in the cement composition, it has significantly reduced costs and environmental pollutants.