CEMENTING MATERIAL FROM CALCIUM CARBIDERESIDUE - RICE HUSK ASH

Kumar Amit VIII Sem. B.E., (CIVIL Engineering)

Department of Civil EngineeringSir MVIT,Bangalore

1. INTRODUCTION :

Calcium Carbide Residue (CCR) is a by-product of acetylene production process (John, 1993),

and its production is described in the following equation:

CaC2+2H2O→ C2H2+Ca(OH)2 ---------------------------------------- (1)

CCR consists mainly of calcium hydroxide, Ca (OH) 2, and is obtained in a slurry form. From

Eqn.1, it is seen that 64 g of calcium carbide (CaC2) provides 26 g of acetylene gas (C2H2) and

74 g of CCR in terms of Ca (OH) 2. Due to its high base, calcium carbide residue was hardly

utilized in any work and all of it went to a disposal area as slurry form as shown in Fig. 1(a)

After being sundries for a few days, the slurry form of calcium carbide residue is changed to

dry form, as shown in Fig. 1(b) Rice Husk Ash (RHA) is derived from the burning of rice husk,

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which is the by-product of rice milling. It was estimated that 1,000 kg of rice grain produced

200 kg of rice husk, after rice husk was burnt, about 20% of the rice husk or 40 kg would

become RHA (Mehta 1986). RHA contains a high amount of SiO2, most of which is in

amorphous form (Gambhir, 1995; Mehta, 1986) which makes RHA a pozzolanic material

according to ASTM C 618 (1997d). Pozzolana as defined by ASTM C 618 (1997d) is a material,

which is siliceous, or siliceous and aluminous material by composition. In general, pozzolana

has little or no cementing property, however when pozzolana has high fineness and in the

presence of moisture, it can react with Ca (OH) 2 at room temperature to provide

property. Upon the cement hydration, the main products are calcium silicate hydrate (CSH),

calcium aluminates hydrate (CAH), and calcium hydroxide, Ca (OH) 2. CSH and CAH are the

cementations materials in the mixture and contribute to the strength of concrete. However,

CSH produces much higher compressive strength than that of CAH, while Ca(OH)2 can react

with SiO2 and Al2O3 from pozzolanic material resulting in additional CSH and CAH in the

mixture, improving some of the properties of the concrete (ACI 232.2R 2000). These improved

properties include increased acid resistance, reduced bleeding, increased compressive strength,

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reduced permeability, etc. (Krammart, et al., 1996) used 30% of CCR and 70% of fly ash by

weight as cementations material of mortar and obtained compressive strengths of 20.9MPa at

90 days. It is believed CCR which is rich in Ca (OH) 2 and RHA which has high SiO2 can react

together by the pozzolanic reaction, resulting in products that would be similar to those

obtained from cement hydration process. Therefore, the objective of this research is to utilize

two waste materials as a new cementing material to substitute Portland cement. In addition,

the utilization of the two materials will reduce the production of Portland cement as well

as reduce the waste disposal volume to make a better environment.

Fig.1 Disposal area of slurry and dry forms of calcium carbide residue: (a) slurry form and (b) dry form

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2. EXPERIMENTAL PROGRAM :

2.1 Materials

Materials used in this experimental program consisted of calcium carbide residue assigned as

CCR, rice husk ash (assigned as RHA), Portland cement Type I, river sand which was passed

sieve No. 16 and retained on sieve No. 100, water, and superplasticizer Type F (naphthalene

base). CCR was collected from the disposal area in the dry form, as shown in Fig.1 (b), and was

sun-dried for 2–3 days to reduce its high moisture content. After sun-dried, the CCR had a

moisture content less than 3% and was then ground by a Los Angeles abrasion machine until

the particles retained on sieve No. 325 less than 10% by weight. Rice husk was collected from

rice mill in Pathumthani province, Thailand, and was burnt to produce in fibrocement

incinerator at approximately 600 to 800°C (Alex, 1981). The RHA was then ground by a Los

Angeles abrasion machine until the particles were as small as those of CCR, i.e., retained on

sieve No. 325 less than 10% by weight.

2.2 PROPERTY OF MATERIALS

Chemical compositions of CCR, RHA, and Portland cement Type I was analyzed by x-ray

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fluorescence spectrometer. Physical properties such as specific gravity, Blaine fineness, material

retained on sieve No. 325, and particle shape of the materials by Scanning electron microscope

were also investigated.

2.3 PROPERTY OF PASTE

Normal consistency and setting times of CCR-RHA pastes were investigated in accordance

With ASTM C 187 (1997b) And ASTM C 191 (1997c), respectively, and compared to those of

Portland cement paste. The ratios of CCR: RHA were varied as 20:80, 35:65, 50:50, 65:35, and

80:20 by weight.

2.4 MIX PROPORTION AND TESTING COMPRESSIVE STRENGTH OF MORTAR:

In this study, the control or standard mortar was a mixture using Portland cement Type I as

cementations material. The rest of the mortars were used as a mixture of CCR and RHA as

cementations material. The mortar contained 1.0 part of cementations material to 2.75 parts

of river sand by weight. The water-cementations material ratio (W/C) was kept at a constant

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of 0.65 in all mixtures. Superplasticizer was employed in order to maintain the flow of mortar

between 110+or-5 since the mixture of CCR-RHA mortars required more water to achieve the

target flow. Table1 gives the mix proportions of all mortars and it is noted that the control mortar has W/C of 0.65 to produce flow of 114 without the adding of superplasticizer. The

procedure to prepare mortar from a new cementing material was the same manner as to

prepare the control mortar. Mortars cube of 5 cm were cast and removed from the molds

after 24 h, then cured in water until the date of testing. Compressive strengths of mortars were

determined at the age of 1, 3, 7, 14, 28, 60, 90, and 180 days of curing.

Table1 Mix proportions of mortar containing a new cementations material (CCR+HRA)

Mortar Calcium

CarbideResidue

RiceHusk ash

Cement Sand Water Superplasticize

Flow

Control 20C80R 35C65R 50C50R 65C35R 80C20R

—2035506580

—8065503520

100—————

275275275275275

656565656565

—5.884.013.893.251.75

114107108113108110

Note: Numbers 20, 35, 50, 65, and 85 in front of the capital C and R mean percentage of

calcium carbide residue and rice husk ash in the mortar mixture, respectively. For example,

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35C65R means mortar containing 35% of calcium carbide residue and 65% of rice husk ash by

weight as cementations material. ‘‘Control’’ means standard mortar.

Table 2: Chemical Compositions of Calcium Carbide Residue, Rice Husk Ash, and Portland cement Type I

Material Chemical composition (%) SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O SO3 LOI

Calcium carbide residue 3.36 2.56 0.33 51.94 0.46 0.03 0.03 0.22 41.72Rice husk ash 78.22 1.48 1.98 4.59 0.62 0.22 2.56 0.43 8.97Cement 20.42 5.78 3.35 63.94 1.06 0.17 0.31 2.29 2.92

3 RESULTS AND DISCUSSION:

3.1 CHEMICAL COMPOSITION:

Table2 presents the chemical composition of CCR, RHA, and Portland cement Type I.

According to chemical composition as specified by ASTM C 618 (1997d), RHA could be classified

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as Class N pozzolana since the sum of SiO2, Al2O3, and Fe2O3 was 81.68% with SO3 of 0.43%

and Na2O of 0.22%. In case of CCR, it had the sum of SiO2, Al2O3, and Fe2O3

as 6.25%, which

was very low. It should be noted that CaO of Portland cement was 63.94% while that of CCR

was 51.94% or about half of the total chemical composition.

Loss on ignition (LOI) of Portland cement, RHA, and CCR were 2.92, 8.97, and 41.72%,

respectively. According to ASTM C 618 (1997d), LOI of natural pozzolanic material Class N shall

not be higher than 10.0%, thus RHA in this experiment meets the requirement. It should be

noted that the LOI of CCR which was determined at the temperature of 950–1000°C was

very high at 41.72%. The LOI of CCR should be very high since the material mainly consists of

Ca (OH) 2 which decomposes into CaO and H2O (gas) at approximately 550°C. The result of

high LOI of CCR was also observed by (Krammart et al., 1996) who found that the LOI of CCR

was 32.27%

3.2 PHYSICAL PROPERTY:

Table3 shows specific gravity and fineness of CCR, RHA, and Portland cement Type I. The

specific gravity of CCR was 2.21 and close to the result obtained from Krammart et al. (1996)

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which was 2.32. The specific gravity of RHA was generally in the range of 2.06 to 2.16 (Min-

Hong and Malhotra 1996), while that of RHA in this research was 2.18. The particle of CCR and

RHA retained on sieve No. 325 (by wet sieve) were 2.52 and 8.64% by weight, respectively,

while Blaine fineness of the materials were 9,630 and 18,050 cm2/g, respectively. The fineness

of RHA in term of Blaine fineness was higher than that of CCR about two times while the

fineness in term of the weight retained on sieve No. 325 was not much different. This result was

due to the higher porosity and irregular shape of RHA particles than those of CCR.

Table 3: Physical properties of calcium carbide residue, rice husk ash and Portland cement type I

3.3 PARTICLE SHAPES OF CALCIUM CARBIDE RESIDUE, RICE HUSK ASH AND PORTLAND CEMENT:

Material Specific Retained Blaine fineness gravity on sieve (cm2/g) No. 325(%)Calcium carbide 2.21 2.52 9,630residueRice husk ash 2.18 8.64 18,050Cement 3.13 9.58 3,230

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Fig.2 shows the particle shapes of CCR, RHA, and Portland cement Type I using scanning

electron microscope (SEM). It was seen that all particles of the materials were irregularly

shaped. Portland cement had solid particle with some rough surface while RHA had rough

surface with high porosity. The surface of CCR was smoother and less porosity than that of

RHA. With high porosity and irregular shape, the CCR and RHA mixture absorbed water into

their particles and resulted in high normal consistency of the CCR-RHA paste.

3.4 NORMAL CONSISTENCY :

Table4 shows normal consistency of cement and CCR-RHA pastes. The normal consistency of

cement paste was 23.9% while those of CCR-RHA pastes were between 43.7% to 62.0%,

depending on RHA content. Paste 80C20R (80% of CCR and 20% of RHA) had normal

consistency of 43.7% and increased to 62.0% in paste 20C80R (20% of CCR and 80% of RHA).

The normal consistency of CCR-RHA pastes needed more water than that of cement paste

because of the high porosity of the two materials as well as the high LOI of CCR. The higher

the RHA content is in the paste, the higher the water is required in the mixture to maintain

the same normal consistency.

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3.5 SETTING TIMES :

Setting times of cement and CCR-RHA pastes are tabulated in Table4. Initial and final setting

times of the cement paste were 107 and 195 min, respectively. The initial setting time of

cement paste was within the allowance specified by ASTM C 150 (1997a), which should not be

less than 45 min. For CCR-RHA pastes, the shortest setting time occurred in paste 50C50R and

the longest setting time was paste 80C20R. The initial and final setting times of paste 50C50R

were 345 and 635 min, respectively, while those of paste 80C20R, the longest setting times,

were 502 and 680 min, respectively. The initial setting time of the new cementing material

was about 3.2 to 4.6 times longer than that of the cement paste. The results suggested that the

ratio of CCR to RHA of 50 to 50% by weight was the suitable ratio to obtain the highest

pozzolanic reaction. In CCR-RHA paste, the Ca (OH) 2 from CCR reacted with SiO2 from RHA

to form CSH while Portland cement reacted with water and formed CSH directly. The long

setting times of calcium carbide residue-rice husk ash paste is because the pozzolanic reaction

between pozzolan and lime is usually much slower than the hydration of cement. Therefore, the

setting times of the new cementitious material must be improved before using in concrete work.

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Fig2 SEM of cementitious materials (a) calcium carbide residue (CCR); (b) rice husk ash (RHA); and (c) Portland cement Type I

Table 4 : Normal consistency and setting times of Portland cement and calcium carbide residue – rice husk ash pastes :

Paste Normal consistency%

Initial setting TimeMinutes

Final setting TimeMinute

Cement 23.9 107 19520C80R 62.0 422 77535C65R 58.8 397 66050C50R 55.8 345 63565C35R 50.6 420 67080C20R 43.7 502 680

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3.6 COMPRESSIVE STRENGTH OF MORTAR :

Compressive strength of CCR-RHA mortars is shown in Table5. Table6 is the relative

compressive strength of CCR-RHA mortars comparing to control mortar. Each datum of the

compressive strength of mortar was obtained from the average of five samples. Compressive

strength of CCR-RHA mortars gradually increased with curing age. The compressive strengths

of CCR-RHA mortars at 1 day were very low and in the range of 0.1 to 0.9 Mpa while that of

control mortar was 8.5 MPa. At the age of 3 days, the compressive strength of CCR-RHA

mortars increased to 1.3 to 5.8 MPa, depending on the mix proportion of CCR and RHA.

Mortar 50C50R was the mix proportion that gave the highest compressive strength. Its

strength was 0.9, 10.0, 15.6, 18.6, and 19.1 MPa, respectively, at the age of 1, 7, 28, 90, and 180

days. Mortar 50C50R had lower compressive strength than that of the control mortar about 9,

2.3, 2.0, 1.8, and 1.8 times at the age of 1, 7, 28, 90, and 180 days, respectively. These results

suggested that the difference of compressive strength of mortar 50C50R and control mortar at

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an early age was very high and reduced to about two times after 28 days. It should be noted

that the mix proportion of the mortar 50C50R did not contain Portland cement and the

strength of mortar was solely contributed from the pozzolanic reaction of the two materials.

Mortar 50C50R contained 50% of CCR and 50% of RHA as cementitious material gave the

highest compressive strength. Increasing or decreasing of CCR content from 50% of the total

cementitious material resulted in lower compressive strength of mortar. For example, mortar

65C35R (65% of CCR and 35% of RHA) had compressive strength of 0.4 and 10.9 MPa at the

age of 1 and 28 days, respectively, or was 4.7 and 35.0% of the control mortar strength. At the

age of 28 to 180 days, the relative compressive strength of mortar 65C35R was almost constant

about 35% of the control mortar strength. When decreased CCR content to 35% of the

cementitious material as in mortar 35C65R, the compressive strength of mortar was 0.4 and

14.6 MPa, at the age of 1 and 28 days, respectively, or was 4.7 and 47.2% of the control mortar

strength.

TABLE 5 : COMPRESSIVE STRENGTH OF MORTAR :

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Mortar 1 day 3days 7 days 14days 28days 60days 90days 180days

Control l 8.5 17.6 23.0 28.3 30.9 32.8 33.7 34.7

20C80R 0.7 5.4 7.0 7.9 9.0 9.7 10.1 10.4

35C65R 0.4 5.8 9.4 12.6 14.6 15.6 15.8 16.7

50C50R 0.9 5.8 10.0 13.6 15.6 1 17.5 18.6 19.1

65C35R 0.4 3.1 7.0 9.9 10.9 11.5 11.9 12.6

80C20R 0.1 1.3 4.0 5.4 6.3 6.7 7.0 7.2

Table6 Relative Compressive Strength of Calcium Carbide Residue-Rice Husk Ash Mortars Compared with Control Mortar

Mortar 1 day 3 days 7 days 14 days 28 days 60days 90days 180days

Control 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

20C80R 8.2 30.7 30.4 27.9 29.1 29.6 30.0 30.0

35C65R 4.7 48.3 40.9 44.5 47.2 47.6 46.9 48.1

50C50R 10.6 32.9 43.5 48.1 50.5 53.3 55.2 55.0

65C35R 4.7 17.6 30.4 35.0 35.3 35.1 35.3 36.3

80C20R 1.2 7.4 17.4 19.1 20.4 20.4 20.8 20.7

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Fig.3 Relationship between compressive strength of CCR-RHA mortars and age

Fig. 4 Relationship between relative compressive strength of CCRRHA mortars and age

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Fig.5 Relationship between compressive strength of CCR-RHA mortars and percentage of RHA

Figs.3 and 4 are plots of results from Tables5 and 6. At the age of 1 to 14 days, the rate of

strength gain was very fast and became slow to almost constant after 60 days. The rate of

strength gain of CCR-RHA and control mortars were similar in behavior, except that the

compressive strengths of the control mortar were higher than that of CCR-RHA mortars at all

ages. Fig.5 suggested that the percentages of RHA between 35 and 65% gave the suitable

results of CCR-RHA mortar to obtain the highest compressive strength. As suggested by Fig.5, it

can be seen clearly that after 7 days the highest compressive strength of mortar is the ratio of

CCR to RHA of 50 to 50%.

4 CONCLUSIONS :

The results of this experiment can be concluded as follows:

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1. Ca (OH) 2 is the major chemical component of CCR and can be mixed with RHA to produce a cementing material;

2. Initial and final setting times of CCR-RHA pastes are too long and need to be shortened

before this cement is adopted for concrete;

3. Mortar containing 50% of CCR and 50% of RHA as cementitious material presented the

highest compressive strength and was 15.6 and 19.1 MPa, at the age of 28 and 180 days,

respectively; and4. Based on the experimental results, the cementitious material of CCR-RHA has a high

potential to be used in concrete work that does not require high compressive strength.

However, more research is needed especially on setting times, early strength, and durability

of concrete made with CCRRHA as cementitious material.

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