Compressive strength performance of geopolymer

Construction and Building Materials 138 (2017) 195–203

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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

Compressive strength performance of geopolymer paste derived from Completely Decomposed Granite (CDG) and partial fly ash replacement Jean-Baptiste Mawulé Dassekpo, Xiaoxiong Zha ⇑, Jiapeng Zhan Department of Civil and Environmental Engineering, Shenzhen Graduate School, Harbin Institute of Technology, 518055, China

h i g h l i g h t s The synthesis of Completely

Decomposed Granite (CDG) with an alkaline activator was investigated. The effect of partial replacement of CDG into fly ash is highlighted. The compressive strength performance of CDG, as a geopolymer new source material was discussed. 100% CDG had a compressive strength of up to 13.89 MPa at 7 days curing period which kept on increasing to 15.77 MPa at 14 days curing period. Completely Decomposed Granite (CDG) can be used as a geopolymer source material.

a r t i c l e

i n f o

Article history: Received 16 November 2016 Received in revised form 24 January 2017 Accepted 30 January 2017

Keywords: Geopolymer Sustainable material CDG Fly ash Compressive strength

g r a p h i c a l a b s t r a c t (CDG)

Fly Ash Green Geopolymer Pastes

Cleaning Oven-drying Sieving

Geopolymerization Na2SiO3

NaOH

a b s t r a c t The compressive strength after the addition of Completely Decomposed Granite (CDG) to fly ash to initiate the polymerization reaction and to form a new geopolymer material was studied. A series of experimental test were performed on 70.7 70.7 mm cubic specimens with full and partial replacement of CDG. The proportion of 0, 10, 20, 30, 50, 70, 80 and 100% of dried CDG soil was mixed with sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) solution to examine the compressive strength behavior. Experimental results showed that the geopolymer paste specimen with 100% CDG as source material had a compressive strength of up to 13.89 MPa. It was found that the Completely Decomposed Granite (CDG) can be synthesized with an alkaline activator and some proportion can be added into fly ash to form a high strength geopolymer mixture. It was also found that the high compressive strength of the combination of CDG-fly ash can be obtained within 7 days curing period but only the CDG compressive strength will keep on increasing over time. Ó 2017 Elsevier Ltd. All rights reserved.

1. Introduction The cement construction industry, in general, these recent years, is confronted with challenges caused by high rate CO2 emissions and the use of alternative materials that is able to replace ⇑ Corresponding author. E-mail addresses: [email protected] (J.-B.M Dassekpo), [email protected] (X. Zha), [email protected] (J. Zhan). http://dx.doi.org/10.1016/j.conbuildmat.2017.01.133 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.

Ordinary Portland Cement (OPC). Despite the progress made on manufacturing processes, the production of OPC remains, until now, responsible for around 6% of all man-made global carbon emissions [1]. Geopolymer is an innovative technology that is making considerable interest in the construction field, particularly in the development of green materials. In contrast to OPC, most geopolymer systems depend on natural or industrial by-products materials containing silicon and aluminium in amorphous form to produce binder agents.

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Table 1 Chemical composition – physical and mechanical properties of the CDG used. Composition Content (%)

SiO2 40.35

Al2O3 30.41

Fe2O3 10.26

FeO 1.84

TiO2 1.00

MnO 0.04

CaO —

MgO —

K2O 1.36

Na2O 0.18

H2O 12.89

Index

x

q

d

e

2.68

0.81

WP % 24.1

IL

Value

WL % 39.2

IP

% 25.5

15.1

0.2

Es MPa 5.4

C kPa 26

u ° 30

g/cm3 1.93

Most of the researches available were describing geopolymer pastes and geopolymer coating materials [2,3]. They placed particular emphasis on the advantages of geopolymer materials such as stronger with high compressive strength, more resistant to corrosion, lower creep and shrinkage properties with better resistance of sulfate attacks and have more possible applications than cement materials. According to the literature, geopolymer can be manufactured as paste, mortar and concrete by using fly ash or industrial waste byproduct materials containing silicon and aluminium in amorphous form. Its compressive strength and Young’s modulus does not change significantly between paste and mortar [4,5]. However, in mortar, compressive strength depends on the strength of the geopolymeric gel, the interfacial bonding between the geopolymeric gel and aggregate and the aggregate itself [5]. In cement mortar, sand or other fine aggregates have a significant influence on its mechanical and rheological properties [6,7]. Geopolymer materials require processes involving high alkalinity solutions, which creates safety risks associated with the high alkalinity of the activating solutions. Therefore, the success of the process is very sensitive to temperature during curing, and the required temperature is dependent upon the source materials and activating solution. Researchers reported that the highest compressive value of geopolymer concrete can be achieved when the temperature is in the range of 60–120 °C [8,9]. Completely Decomposed Granite (CDG) is the most residual soils found in many parts of the world, especially in South China, Shenzhen city. CDG soil has been used extensively in construction for deformation and stability of slopes, retaining walls, excavations works, deep and shallow foundations or as construction materials because of it stress-strain-strength behavior [10]. This waste material is very abundant in recent years because of the many metro and underground rails construction projects initiated by the government. It has now become a danger and a cause for worry for the local government and the people at large, because it has caused many landslides including the landslide observed some months ago in the city of Shenzhen. Most researches on CDG soil [11–14] was performed to study the mechanical behavior on the fines contents, and few researches have been done on the compressive strength of the material. For example, Nagaraj et al. [11] studied the influence of plastic fines on the permeability of soil by mixing sand with medium kaolin clay. Naeini et al. [12], in the same direction, also studied the strength effect of fines content on the mixed and layered samples. The experimental results indicated that the relative density at which the transition occurs, increased with fines content. Daehyeon Kim et al. [13] also evaluated the mechanical properties of the fine aggregate content of the compacted decomposed granite soils by developing direct shear and triaxial shear laboratory tests. The results of the triaxial tests indicated that as the fine aggregates percentage decreased, the cohesion decreased, at the same time, the internal friction angle increased. The results for the direct shear test also demonstrate that soils containing lower amounts of fine aggregates have the shear strength largely reduced after they reach their peak value. Shanyong Wang et al. [14] investigated the effect of fines content on dynamic compaction grouting and found that, the compaction efficiency of CDG increases with increasing fines content, and can reach peak compaction efficiency when the fines content reaches a certain percentage.

K cm/s 1.8 105

Up until now, there have not been any researches on the use of this material in geopolymer studies. The aforementioned information motivates the authors to combine this material with fly ash in the development of geopolymer paste that is environmentally friendly (i.e. does not produce CO2), cost efficient (i.e. it’s basically free and easy to acquire) and of storing it in large quantities at construction sites which tend to become an endangerment to the people living nearby especially when it rains heavily. Consequently, the present research work was carried out to characterize the effect of full or partial replacement of CDG into fly ash, and to evaluate its capability to be synthesized in the presence of an alkaline activator by comparing the compressive strength values. 2. Materials characterization and experimental methods 2.1. Materials characterization 2.1.1. Completely Decomposed Granite (CDG) A typical residual soil, Completely Decomposed Granite (CDG) from Shenzhen plant in China was used in the present study. Xray diffraction (XRD) test was conducted on the whole CDG soil, and the data was analyzed. The chemical compositions and the physical and mechanical properties were listed in Table 1. It can be seen that the CDG soil used in this research work covers a large range of particle sizes mainly composed of silica and alumina. In order to obtain the particle size distribution of the soil, the CDG was firstly cleared of any industrial waste and oven-dried at 105 °C for 24 h (Fig. 1). After the above treatments, dry sieving was performed using electric sieve shaker (Fig. 2) and particles larger than 5 mm were discarded. Afterwards, sieving method and hydrometer method were then used to get the particle size distribution (PSD) curve as shown in Fig. 3. 2.1.2. Fly ash and activator solutions In this study, locally available low calcium Class F fly ash from a thermal power station in Shenzhen that conforms to ASTM C-618 specification was used throughout the research. The particle size distribution of fly ash used is provided in Fig. 4. The activator solution used for the geopolymerization process is a combination of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). The solutions were prepared by mixing sodium hydroxide in pellets form in sodium silicate solution and water as shown in Fig. 5. Same to the CDG soil, X-ray diffraction (XRD) was also performed to investigate the chemical composition of the fly ash and the results are shown in Table 2. It can be observed that the content of calcium oxide is very low; therefore it can be classified as Class-F fly ash according to ASTM C618-08 [15]. It can also be seen that, the content of oxides of silicon and aluminium is relatively high with 60.70% and 24.72% respectively. 2.2. Experimental methods 2.2.1. Mix design proportion This laboratory investigation adopted the mixture proportion present in Table 3. Note that the concentration of sodium hydroxide solution can be measured in terms of molarity and the value of (14 M) concentration of NaOH was assumed to reach a higher value

197


Fig. 1. CDG dried conditioning.

100

120

80

100

Cumulative passing (%)

Cumulative passing (%)

Fig. 2. CDG sieving materiel.

60

CDG

40 20

80

Fly ash

60 40 20

0 0

1

2

3

4

Particle-size (mm) Fig. 3. Particle size distribution (PSD) of CDG.

5

0 0.1

1

10

100

Particle-size (microns) Fig. 4. Particle size distribution (PSD) of fly ash.

1000

198


Fig. 5. Sodium silicate solution and sodium hydroxide pellets.

Table 2 Chemical composition of the fly ash used. Composition Content (%)

SiO2 60.70

Al2O3 24.72

Fe2O3 6.90

CaO 0.70

MgO 1.13

TiO2 —

MnO —

K2O —

P2O5 —

SO3 1.50

LOI 2.35

Table 3 Geopolymer paste mixture proportion. Specimen Id.

CDG (%)

CDG (g)

Fly ash (g)

Mixture Alkaline Activator

GP.Fly ash GP.1C GP.2C GP.3C GP.5C GP.7C GP.8C GP.CDG GP.AA0

0 10 20 30 50 70 80 100 100

0 70 140 210 350 490 560 700 700

700 630 560 490 350 210 140 0 –

Sodium Hydroxide Solution (NaOH) of 14 M

Sodium Silicate Solution (Na2SiO3) in (g)

28.35 28.35 28.35 28.35 28.35 28.35 28.35 28.35 –

176.70 176.70 176.70 176.70 176.70 176.70 176.70 176.70 –

of compressive strength [16]. On the other hand, the alkaline activator and fly ash (AL/FA) ratio adopted in this study follows the research work of [17] and serves as the basis of the mixture constituents calculation. The replacement of CDG was taking to investigate its performance in the mixture.

Water (g)

Plasticizer (g)

650 650 650 650 650 650 650 650 650

10 10 10 10 10 10 10 10 10

were released from the molds and left alone at room temperature for 7 and 14 days respectively. 3. Experimental results and discussion 3.1. Compressive strength test data

2.2.2. Specimens manufacturing and curing process The manufacturing procedure used for fly ash-based paste is similar to that of CDG-based paste. The first step was the mixing of sodium silicate solution, sodium hydroxide pellets and water basing on predefined mix proportions to make an alkaline activator. The rotating pan mixer with rotating blades was used for preparing geopolymer mix. Afterwards, fly ash and Completely Decomposed Granite with the alkaline activator, plasticizer and additional water is mixed in the pan mixer for about five to six minutes to get a homogeneous paste (Fig. 6a–d). Casting of plastic cubes molds with 70.7 70.7 70.7 mm size was performed and placed on a vibration table for 2–3 min to remove entrapped air in the mix. After four hours rest period, the specimens were released from the molds and left alone at room temperature for thermal curing at 60 °C and 50%RH for 7 and 14 days respectively, the time which the compressive test was performed using compressive machine as shown in Fig. 7. This temperature value was chosen because [18,19] found that the curing temperature and the time have a great influence on the strength. The specimens

Table 4 summarizes the results obtained from the compressive testing of fly ash-based paste and CDG-fly ash at different proportions for a curing period of 7 and 14 days. The compressive strengths values were calculated after the compressive test using Eq. (1).

rc ¼ P=A

ð1Þ

where, P = Load applied (kN), and A the specimen pressed area (mm2). For better comparison of the experimental results, beside the partial replacement of CDG, the full replacement of fly ash with alkaline solution specimen was also performed. Also, to verify the geopolymerization capability of the material, a CDG specimen was mixed without an alkaline activator. The values of the compressive strength of each geopolymer paste specimen are also included in the table. It can be observed that the compressive strengths of the geopolymer paste specimens are in the range of 4.62–18.42 MPa for a curing period of 7 days while their value is


199

Fig. 6. Fresh geopolymer pastes: (a) CDG paste without alkaline activator; (b) CDG paste with alkaline activator; (c) CDG-Fly ash based geopolymer; (d) Fly ash based geopolymer.

in between 3.75 and 16.30 MPa for curing period of 14 days. Also, the compressive strength of the CDG paste without an alkaline activator for a curing period of 7 and 14 days is respectively 0.36 MPa and 0.43 MPa. It was noticed that the compressive strength at 7 days curing time of the specimen with 100% fly ash presents the highest compressive with 18.42 MPa, followed the specimen with 100% CDG with strength up to 13.89 MPa. This high rate compression involves the capacity of the Completely Decomposed Granite (CDG) to be synthesized in the presence of sodium Hydroxide (NaOH) and sodium silicate (Na2SiO3) to form geopolymer paste. 3.2. Compressive load - deformation curves

Fig. 7. Compressive strength test set-up.

Fig. 8 shows the curves related to the compressive loaddisplacement relationship of the tested geopolymer paste specimens at different curing times of 7 and 14 days with varying of CDG and fly ash proportions. It can be seen from Fig. 8 curve shape that the tested specimens remain linearly elastic throughout the test until failure. It can be observed in the geopolymer pastebased CDG partial replacement curve that, the failure occurs after the compressive load reached an average of 10 kN for most of the specimens except the specimens with 10% of CDG and fly ash-based geopolymer which started early. In both cases, the curve displayed a sudden drop of the compressive loading which indicates that these two materials are a brittle type of material when they are used in terms of geopolymer paste. This behavior is remarkable on 90%, 100% fly ash-based geopolymer paste and 100% CDG-based geopolymer paste at a curing period of 7 and 14 days. The peak load average of these three specimens under compressive loading at 7 days curing time is 69.46 kN, 91.75 kN

200


Table 4 Summary of compressive strength values of geopolymer paste specimens. CDG (%)

Fly ash (%)

GP.Fly ash GP.1C GP.2C GP.3C GP.5C GP.7C GP.8C GP.CDG GP.AA0

0 10 20 30 50 70 80 100 100

100 90 80 70 50 30 20 0 0

7 days curing

Compressive strength (MPa)

18.42 13.87 9.75 7.57 6.73 6.72 4.62 13.89 0.36

16.30 12.52 6.84 5.83 5.36 4.38 3.75 15.76 0.43

100000

70000

90000

60000 50000 40000 30000 GP.1C GP.2C GP.3C GP.5C GP.7C GP.8C

20000 10000

14 days curing

Compressive strength (MPa)

80000

Compressive load (N)


Specimen Id.

80000 70000 60000 50000 40000 30000 20000 GP.Fly ash GP.CDG

10000

0

0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0

0.5

1.0

Displacement (mm)

1.5 2.0 2.5 Displacement (mm)

3.0

3.5

a) Geopolymer paste-based CDG partial replacement at 7 days curing (b) Geopolymer paste-based Fly ash and CDG at 7 days curing 90000

70000

80000



60000 50000 40000 30000 GP.1C GP.2C GP.3C GP.5C GP.7C GP.8C

20000 10000

70000 60000 50000 40000 30000 20000 10000

0

GP.Fly ash GP.CDG

0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Displacement (mm)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Displacement (mm)

c) Geopolymer paste-based CDG partial replacement at 14 days curing (d) Geopolymer paste-based Fly ash and CDG at 14 days curing Fig. 8. Compressive load-deformation curves of tested specimen at 7 and 14 days curing time.

and 88.58 kN with a failure displacement of 2.34 mm, 2.71 mm and 1.64 mm respectively. Similarly, the peak compressive load at 14 days curing period is in the range of 62.62 kN, 81.25 kN and 79.95 kN with a failure displacement of 3.12 mm, 3.26 mm and 1.57 mm respectively. It can be seen that peak load at 7 days curing time is between 69.46 kN and 91.75 kN with a failure displacement around 1.64–2.71 mm unlike average peak load between 62.62 kN and 81.25 kN with a failure displacement around 1.57–3.26 mm for the curing period of 7 and 14 days specimens.

3.3. Failure mode of the CDG fly-ash based geopolymer paste under compressive loadings The failure mode pattern observed in this experimental test is generally the same for all specimens tested under compressive loadings. The common failure under compression observed for the majority of specimens is splitting, shear and conical. These types of failures were also observed in the specimens with occurrence of crack along the lateral faces of the specimens. Fig. 9 shows

201


18 GP.Fly ash

Casted specimens

Compressive Strength (MPa)

16

Specimens failure patterns

GP.CDG

14 days curing time 14 GP.1C

12 10 8

GP.2C

6

GP.5C GP.3C

GP.7C

4

GP.8C

0

10

20

30

40

50

60

70

80

90

100

Completely Decomposed Granite proportion (%) Fig. 11. Compressive strength versus CDG proportion curve of the specimens at 14 days curing time.

Compressed FA specimen

Compressed CDG specimen

Fig. 9. Casted specimens before and after testing and typical failure patterns.

20 GP.Fly ash


18

7 days curing time 16 14

GP.CDG

GP.1C

12 10

GP.2C

8

GP.3C

GP.7C

GP.5C

6 4

GP.8C

0

10

20

30

40

50

60

70

80

90

100

and the reason is the amount of gel formed during the geopolymerization process is not enough to glue all CDG-Fly ash fine particles, therefore leads to a premature failure during loading which results in the reduction of its strength. In general, the appearance of the curve can be described by four distinct points: for the specimen with 10% CDG, the compressive strength is up to 13.87 MPa for 7 days curing time (Fig. 9) while 12.52 MPa for 14 days curing time (Fig. 10). Which means that, at this percentage, the specimen can resist compression for at least 12 MPa. It can be observed that the reduction of the strength from 20% CDG replacement is more rapid in both cases compared with the 10% CDG proportion. The strength for 30, 50, and 70% of CDG seems to have approximate strengths values. The values of 7.57, 6.73, and 6.72 MPa was assumed respectively for a curing period of 7 days and 5.83, 5.36, and 4.38 MPa compressive strengths for 14 days curing period. In conclusion, the CDG soil can be added to fly ash at these three percentages without large changes to its compressive strength because of the tiny difference strengths observed. In the case of 80% CDG replacement, a drop was observed in the strength under compressive loading when increasing CDG quantity as the strength reached values of 4.62 and 3.75 MPa respectively for 7 and 14 days. This indicates that the amount of gel at this stage was not enough to glue CDG particles and to ultimately lead to geopolymerization process.

Completely Decomposed Granite proportion (%) Fig. 10. Compressive strength versus CDG proportion curve of the specimens at 7 days curing time.

the casted specimens before and after testing and the typical failure patterns. 3.4. Effect of the partial replacement of CDG on the compressive strength The graphs describing the effect of varying the proportion of Completely Decomposed Granite (CDG) and fly ash (FA) with their strengths for 7 and 14 days curing period are shown in Figs. 10 and 11. From the curve, it can be observed that, the compressive strength of geopolymer paste-based CDG specimen decreases with increasing proportion. This was very remarkable even if it was cured for 14 days. Concerning this result, it is clear that there is a drop in compressive strength with the increase in CDG content

3.5. Comparison of compressive strength of CDG-based geopolymer and CDG without alkaline solution The comparison of the compressive strength of CDG-based geopolymer and CDG without addition of alkaline solution was also conducted and shown in Fig. 12. The values of the compressive strength at 7 and 14 days curing time are 13.89 MPa, 15.76 MPa, 0.36 MPa and 0.43 MPa respectively for CDG-based geopolymer and CDG without addition of an alkaline solution. It is evident that the alkaline solution in the mixture greatly influenced the compressive strengths. The presence of sodium hydroxide (NaOH) and sodium Silicate (Na2SiO3) solutions in the paste is substantial and notable since the specimen without alkaline activator presents the lowest strengths. The success of using CDG, which is considered as a residual material in the formation of geopolymers is much appreciated since it is comparably free or cheaper than fly ash and presents good filler particle sizes. This indicates that a full quantity of CDG soil with an alkaline solution not only gives high

202


CDG-based geopolymer

20

CDG without alkaline activator

15.77

16



18

13.89

14 12 10 8 6 4 2

0.43

0.36

0 0

7

14

21

Curing time (Days)

20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3

7 days curing time 14 days curing time

GP.FA GP.1C GP.2C GP.3C

GP.5C

GP.7C GP.8C

GP.CDG

Fig. 14. Comparison of the compressive strengths at different curing time.

Fig. 12. Compressive strength of CDG-based geopolymer and CDG without alkaline solution.

strength but provides maximum economic solutions which leads to environmental protection.

geopolymer paste. We can derive from this result that the compressive strength of the CDG specimen is reaching progressively the fly ash specimen. Conclusively, the Completely Decomposed Granite (CDG) is a material which can increase its compressive strength over time.

3.6. Comparison of compressive strength of full CDG and fly ash based geopolymer

3.7. Comparison of the compressive strength at different curing time

The values of the compressive strength at 7 and 14 days curing time for the full CDG and fly ash-based geopolymer paste are in the range of 13.89–18.42 MPa (Fig.13). By looking at the graph, the compressive strength of the fly ash-based paste presents a high value of 18.42 MPa at 7 days curing time. In the case of CDGbased paste, the value of the compressive strength at 7 days curing is 13.89 MPa, which is largely sufficient to confirm that the CDG particle has been synthesized with the alkaline solution to form the geopolymer paste. On the contrary, the compressive values of these two types of specimen at 14 days demonstrate a decrease in strength, around 12% (16.30 MPa) for the fly ash-based geopolymer paste but an increase in strength of about 12% (15.76 MPa) for the CDG-based CDG-based paste

20

Fly ash-based paste

18.43


18

16.30 15.77

16 13.89

14 12

Fig. 14 presents the comparison of the compressive strengths of the specimens at different curing times. As indicated in the figure, the average compressive strength of fly ash-based paste is 18.42 MPa and the CDG-based paste value is 13.89 MPa at 7 days curing period respectively and 16.30 MPa and 15.76 MPa at 14 days curing respectively. These values represent the highest strengths values obtained from this experimental tests when compared to others. This does not mean that the other compressive strengths values are negligible. They must be taken into account as the all the specimens were a manufactured as paste by using very fines size particles. On the other hand, the compressive strength values of the geopolymer specimens at 7 and 14 days is significant and is marginally higher as the specimens were manufactured as paste and cured at a controlled temperature of 60 °C. If we take the average of their compressive strength values at 7 days and 14 days; it follows that the compressive strength values from geopolymer paste in this study is higher than that of cementbased mortar. From this result, it can be concluded that the geopolymer paste can equalize or even outperform cement-based mortar in terms of strength under compressive loading. This result is largely acceptable compared to the results reported by other researchers [7,20,21] on the strength of geopolymer paste, mortar and cement-based mortar specimens.

10 8

4. Conclusions

6

This research work presents the experimental investigation on the compressive strength after the use of full Completely Decomposed Granite (CDG) to activate a geopolymerization process and the addition at some proportions of the same material to fly ash. From the experimental results, the following conclusions can be drawn:

4 2 0 0

7

14

21

Curing time (Days) Fig. 13. Comparison of compressive strengths of CDG-based and fly ash-based pastes.

(a) Compressive strengths of up to 13.89 MPa and 18.42 MPa can be obtained from the mixture respectively for CDG and Fly ash-based geopolymer pastes at 7 days curing time.


(b) The Completely Decomposed Granite (CDG) based geopolymer paste can achieve a compressive strengths of up to 13.89 MPa and 15.76 MPa respectively at 7 and 14 days curing time without addition of fly ash. These values prove that the Completely Decomposed Granite (CDG) is a material which can be used as geopolymer source material. (c) The fly ash and the CDG-fly ash based geopolymers can reach high compressive strengths within some few days, but CDG-based geopolymer’s compressive strength keeps increasing over time. This indicated that CDG-based geopolymer obtains a high compressive strength gradually. (d) The proportions of 10, 20, 50 and 100% CDG replacement were identified as the most significant additional ratio for the preparation of the mixture. Based on the conclusions stated above, it will also be very urgent to conduct specific research on Completely Decomposed Granite (CDG) soil in order to characterize the material strength behavior as a geopolymer green component for its potential adoption in the long term. Acknowledgements This research is funded by the National Nature Science Foundation of China (Grant Number: 51578181) and Shenzhen Science and Technology Plan Project (No JCYJ20150327155221857). Acknowledgement is also given to Shenzhen Carbon Storage Cement-based Materials Engineering Laboratory. References [1] M.S. Imbabi, C. Carrigan, S. McKenna, Trends and developments in green cement and concrete technology, J. Sustainable Built Environ. 1 (2012) 194– 216. [2] J. Davidovits, Geopolymers: inorganic polymeric new materials, J. Therm. Anal. 37 (1991) 1633–1656. [3] A. Palomo, M.W. Grutzeck, M.T. Blanco, Alkali-activated fly ashes – a cement for the future, Cem. Concr. Res. 29 (8) (1999) 1323–1329.

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