
==== Front
ACS Omega
ACS Omega
ao
acsodf
ACS Omega
2470-1343
American Chemical Society

10.1021/acsomega.4c06129
Article
Influence of Temperature and Humidity on Mechanical Properties of Calcined Oyster-Shell Powder-Modified 3D-Printed Concrete
Wei Yazhi
https://orcid.org/0000-0002-0680-6916
Zhang Hui *
School of Mechanical Engineering and Automation, Dalian Polytechnic University, Liaoning 116034, China
* Email: zh1226419340@163.com.
05 09 2024
17 09 2024
9 37 3918039187
02 07 2024
28 08 2024
15 08 2024
© 2024 The Authors. Published by American Chemical Society
2024
The Authors
https://creativecommons.org/licenses/by-nc-nd/4.0/ Permits non-commercial access and re-use, provided that author attribution and integrity are maintained; but does not permit creation of adaptations or other derivative works (https://creativecommons.org/licenses/by-nc-nd/4.0/).

Calcined oyster-shell-powder-modified concrete (CS), developed by our research group, is an ecological quick-setting concrete suitable for 3D printing technology. It has been discovered that the material’s formability is obviously affected by ambient temperature and humidity after the 3D printing process, and this phenomenon also occurs in other 3D-printed concrete materials. To figure out the influence laws of temperature and humidity on the mechanical properties of CS-modified 3D-printed concrete during the curing time, the methods of both microanalysis and macro testing are applied. The molecular dynamics method is used to reveal the effects of temperature and humidity on the material’s mechanical parameters, including elastic modulus, bulk modulus, and shear modulus. The macroscopic compressive strength and flexural strength of the 3D-printed concrete are measured to validate microanalysis findings. Results show the most suitable curing conditions for improving the mechanical properties of CS-modified 3D-printed concrete are the ambient temperature of 20 ± 1 °C and the relative humidity of 80–95%. Under this curing condition, the 28 day flexural strength of CS-modified 3D-printed concrete can reach 14 MPa, and the compressive strength can reach 44 MPa, which significantly improves the strength of printed samples.

National Natural Science Foundation of China 10.13039/501100001809 52205338 Liaoning Province NA LJBKY2024009 Dalian Jinshiwan Laboratory NA Dljswkf202405 Foundation of Liaoning Province Education Administration 10.13039/501100010086 JYTMS20230438 Natural Science Foundation of Liaoning Province 10.13039/501100005047 2023-BS-177 document-id-old-9ao4c06129
document-id-new-14ao4c06129
ccc-price
==== Body
pmc1 Introduction

3D concrete printing is a promising construction technology in line with the development concept of green architecture, which has the characteristics of saving materials, reducing labor input, and providing flexible operation.1,2 This technology is gradually emerging in the fields of landscaping, bridge embankment, and house construction.3−6 Following the gradual application of 3D printing concrete techniques, people are increasingly seeking material innovation, especially reusing natural wastes.7,8 Navaratnarajah suggested that peanut shell ash can be used as a partial replacement for cement.9 Colyn used fly ash, silica fume, slag (GGBS), and metakaolin (MK60) as alternative binders to demonstrate the sustainability of the enhanced 3D-printed concrete.10 Based on this, our group proposed a sustainable oyster-shell derivative as an alternative to OPC to fabricate a novel biomass-based 3D-printed concrete: calcined oyster-shell powder (CS) modified concrete.11 The compressive strength and flexural strength of 3D-printed concrete parts exceeded 40 and 10 MPa, respectively, after 28 days.

To make further improvements in the mechanical properties of the 3D-printed parts using CS-modified concrete, the research focuses on the early curing conditions of the printed parts. A large number of experimental studies were carried out to investigate the effects of temperature and humidity on the mechanical properties of concrete formwork, considering various aspects including pore structure,12 temperature difference,13 water content,14 shrinkage cracking,15 etc. It has been revealed that temperature and humidity of the curing environment are the key influencing factors.16−19 As for 3D-printed concrete parts, they not only serve in different construction environments but also suffer from higher early water loss and drying shrinkage during their rapid prototyping process, making them more susceptible to severe hydration reaction stagnation. This poses a serious challenge to strength development of 3D-printed concrete.20−22 Therefore, it is of great significance to study the influence of the rules of temperature and humidity on the mechanical properties of 3D-printed concrete. This is crucial for achieving accurate maintenance of concrete parts and predicting and preventing the deterioration of properties caused by temperature and humidity. Molecular dynamics simulation is a powerful tool to study the microkinetic behavior of CS-modified concrete under the influence of temperature and humidity.23−25 This simulation can not only help to understand the microstructure evolution of CS-modified concrete under specific environmental conditions but also can predict the change of its macroscopic mechanical properties, thus revealing the mechanism of temperature and humidity’s microscopic influence on 3D-printed concrete.

Given the above phenomenon, this article will focus on exploring the effects of temperature and humidity on the mechanical properties of CS-modified 3D-printed concrete. At the microscopic level, the molecular dynamics research method is used to analyze the effects of the temperature and humidity on the mechanical properties of the C–S–H gel system. At the macroscopic level, the mix-stir-extrusion integrated 3D concrete printing is used to prepare concrete specimens and to study the evolution of their compressive strength and flexural strength with temperature and humidity. Ultimately, this paper reveals the effect of the temperature and humidity on the hydration reaction of CS-modified concrete and strives to provide a curing theoretical basis for further application of CS-modified 3D-printed concrete.

2 Results and Discussion

2.1 Radial Distribution Function

The radial distribution function (RDF) curve of the C–S–H model shown in Figure 1 proves that the RDF of the constructed molecular model conforms to the characteristics of the amorphous system: short-range ordering and long-range disordering. It indicates that the constructed C–S–H molecular model is reasonable.

Figure 1 RDF curve of C–S–H.

2.2 Effects of Temperature on the Mechanical Properties of 3D Printed Concrete

2.2.1 Molecular Simulation Results and Analysis

The effect of different temperatures on the mean square displacement (MSD) varies in the C–S–H system, as shown in Figure 2a. The research results show that the MSD value and slope also increase with the temperature rise. This indicates that both the diffusion coefficient and diffusion rate tend to increase with rising temperatures. However, at certain temperatures, such as 42 °C, this trend may be influenced by changes in the internal properties of the system, resulting in different diffusion behaviors. 21 °C is in the middle of the range, with a moderate rate of molecular diffusion. Too fast a diffusion rate may lead to uneven distribution of hydration products, and internal stresses at a slow rate may affect the early strength development of the concrete. In Figure 2b, the MSD curves at different temperatures tend to be consistent, and the effect of temperature on the C–S–H/CaO system is not significant. In addition, the overall MSD value of the C–S–H system with the addition of CaO rises sharply, indicating that the molecular movement in this system is more intense. The reason for this phenomenon is that the hydration of CaO promotes the generation of Ca (OH)2, which is an exothermic process that raises the heat of hydration and makes the molecules in the system more active.

Figure 2 MSD curves of two materials at different temperatures: (a) C–S–H and (b) C–S–H/CaO.

Figure 3 demonstrates the mechanical parameters of the C–S–H system (Figure 3a) and the C–S–H/CaO system (Figure 3b) at different temperatures. From Figure 3a, the mechanical parameters reach the highest at 21 °C, and the theoretical comprehensive mechanical properties are the best. Both excessively low and high temperatures can affect the mechanical properties development of C–S–H. The overall mechanical parameters are significantly improved compared to the C–S–H system after the addition of CS, and the sensitivity of mechanical properties to temperature is reduced (Figure 3b).

Figure 3 Simulation result curves of mechanical properties with two materials at different temperatures: (a) C–S–H and (b) C–S–H/CaO.

2.2.2 Macro-Test Results and Analyses

Figure 4 provides evidence that 3D-printed concrete achieves optimal mechanical properties at 21 °C. Regardless of Material 1 and Material 2, the mechanical strength of Group A2 is far superior to that of the other groups. When the 28 day mechanical strength of Group A1 of Material 1 was set as the control group, we observed that the flexural strength of the other three groups was increased by 43.30, −29.21, and 17.06%, respectively. The compressive strength was increased by 43.11, −6.29, and −1.81%, respectively. Similarly, in Material 2, compared with Group A1, the flexural strength of the other three groups was increased by 54.32, −10.18, and 10.87%, respectively. The increase in compressive strength was 65.40, −14.06, and 11.43%, respectively. The results indicate that low temperatures are not suitable for curing 3D-printed concrete under high-humidity conditions. Although increasing the temperature can enhance the mechanical properties of concrete, temperatures of >42 °C are also unsuitable for curing.

Figure 4 Flexural and compressive strength of 3D-printed concrete specimens under different temperature conditions: (a) Material 1 flexural strength, (b) Material 1 compressive strength, (c) Material 2 flexural strength, and (d) Material 2 compressive strength.

Combined with Figures 3 and 4, maintaining a curing temperature of 20 ± 1 °C can optimize the mechanical properties of 3D-printed concrete under high-humidity conditions. The appropriate curing temperature can balance the hydration rate and water evaporation, thus achieving stable performance development. The low temperature slows the diffusion of water in the 3D-printed concrete, impeding hydration and precipitation of the hydration products. However, excessive temperatures will accelerate water evaporation, increase the porosity, and reduce the mechanical strength of concrete. The addition of CS increases the CaO content, promotes the hydration of C–S–H through the formation of Ca (OH)2, and partially compensates the influence of temperature on mechanical properties.

2.3 Effects of Humidity on the Mechanical Properties of 3D Printed Concrete

2.3.1 Molecular Simulation Results and Analysis

Figure 5 represents the results of mechanical properties performed by the C–S–H (Figure 5a) and C–S–H/CaO (Figure 5b) models with different water contents. Figure 5a shows that there is a positive correlation between the increase in the mechanical parameters and the increase in the water–calcium ratio between 0.4 and 0.8. However, as the water-to-calcium ratio varies from 0.8 to 0.98, the mechanical parameters exhibit a slight decrease. Figure 5b shows that the overall mechanical parameters no longer change significantly with the increase of the water–calcium ratio. However, when the water–calcium ratio is 0.8, the trend change point appears, and when the water–calcium ratio gradually approaches 0.98, the mechanical parameters decline faster. The reasons for this phased change are mainly the following two aspects: on the one hand, when the water–calcium ratio is low, the internal humidity cannot provide enough water molecules, and the hydration reaction is significantly inhibited. Due to the constant exchange of water with the outside world during the solidification process of concrete, as the ambient humidity increases, more water molecules enter the concrete to participate in the hydration reaction, which promotes the hydration reaction to a certain extent. On the other hand, too much water content in the concrete structure leads to a decrease in interlayer adhesion and mechanical properties.

Figure 5 Curve of simulation results of mechanical properties with different water content: (a) C–S–H and (b) C–S–H/CaO.

2.3.2 Macro-Test Results and Analyses

Figure 6 summarizes the humidity dependencies of flexural strength (Figure 6a,c) and compressive strength (Figure 6b,d). The results show that increasing humidity gradually improves the mechanical properties of the 3D-printed concrete specimen. In particular, the flexural strength is relatively significantly affected by humidity, and the flexural strength of Group B4 in Material 2 is even more than twice that of Group B1. However, compared to Material 1, the rate of change in the mechanical properties of Material 2 with humidity is slower. It mainly reflected in the improved mechanical strength at 1- and 3 days, indicating that the early mechanical properties of 3D-printed concrete with CS become more stable.

Figure 6 Flexural and compressive strength of 3D-printed concrete specimens under different humidity conditions: (a) Material 1 flexural strength, (b) Material 1 compressive strength, (c) Material 2 flexural strength, and (d) Material 2 compressive strength.

Based on Figures 5 and 6, the optimal curing humidity is 80–95%. Under dry conditions, water molecules are reduced, the early hydration process of concrete is inhibited, and the rate of the hydration reaction are reduced. This leads to the nonuniform dispersion of hydration products and reduced interaction between C–S–H, which is not conducive to the development of mechanical properties of 3D-printed concrete. In addition, CaO, as a water retention material, can help the concrete retain more water, which plays the role of “internal curing” of concrete specimens. Therefore, to obtain the best concrete properties, a sufficient water supply should be ensured during the curing process.

In this research, the simulation results of the two models may deviate slightly from the experimental results. This discrepancy is attributed to the fact that factors such as the presence of pores in the concrete specimens encountered in actual testing were not considered during the analysis, resulting in a certain degree of deviation between the simulation results and the experimental results.

3 Conclusions

Suitable curing temperature and humidity can prevent mechanical property degradation of 3D-printed concrete during curing. Based on the molecular motion behavior and macro test analysis, the mechanical properties of calcined oyster-shell powder (CS)-modified 3D-printed concrete under different temperatures and humidity conditions were studied. The results are:(1) Calcium oxide in CS participates in the hydration reaction and intensifies the hydration heat, reducing the temperature sensitivity of 3D-printed concrete to a certain extent. Moreover, the addition of CS enables the combination of “internal curing + external curing” of 3D-printed concrete, which improves the effect of water shortage.

(2) Setting the curing temperature at 20 ± 1 °C and maintaining a relative humidity of 95% enhance mechanical properties in 3D-printed concrete. Low-temperature curing prevents rapid water loss and dry shrinkage cracks, while high-temperature curing requires cautious control of heating and cooling rates to avoid compromising mechanical properties. Adequate humidity conditions ensure a steady supply of water molecules, facilitating continuous and stable hydration.

(3) Molecular dynamics analyses of the C–S–H system corroborated these results. The combined mechanical parameters of the molecular system are optimal at room temperature and high humidity, and the molecular diffusion rate is moderate at 21 °C, which is favorable for the precipitation of hydration products. Higher water-to-calcium ratios have been shown to favor the modulus of elasticity. This combination enables the concrete hydration to reach a stable equilibrium state, ultimately promoting the 3D-printed concrete to attain superior mechanical strength.

4 Material and Methods

4.1 Raw Material

Two distinct concrete materials were designed in this article, primarily utilizing two kinds of cement, fine aggregate, and calcined oyster-shell powder (CS) as their primary components. Two types of cement were used as bonding materials: P. O42. Five ordinary Portland cement (OPC) and R. SAC42.5 sulfate aluminate cement (SAC). The fine aggregate was made of natural river sand with a partial size of 1.3 mm. CS was made of waste shells after grinding and then calcined at 900 °C for 40 min to produce a white powder product with a CaO content of 95% or more. Polycarboxylate superplasticizers (SP), hydroxypropyl methylcellulose (HPMC), and attapulgite (ATP) were selected as admixtures to improve the printability of 3D-printed concrete.

The specific ratios were decided by the pre-experiment (Table 1). The raw materials were placed in a multifunctional mixer to be well mixed for 10 min at the speed of 40 rpm.

Table 1 Specific Ratios of 3D Printed Concrete (Unit: g)

 	OPC	SAC	CS	water	sands	SP	HPMC	ATP	
1	250	250	0	170	600	1.20	0.50	5.00	
2	190	250	60	170	600	1.20	0.50	5.00	

4.2 3D Printing Concrete Process

The mix-stir-extrusion integrated 3D printing concrete equipment was selected for printing concrete specimens. It consists of a material transfer system, a printing nozzle, and an associated control system. The printable space of the printing device is 1.5 × 1 × 0.5 m, and the diameter of the nozzle outlet is 22 mm. The material transfer system transported the dry material to the printing nozzle with the inflow rate of water controlled by a flow meter. The printing process is shown in Figure 7.

Figure 7 Printing process of 3D printing concrete equipment.

4.3 Testing Methods

4.3.1 Modeling

At the molecular scale, calcium silicate hydrate (C–S–H gel) is the “bridge” of concrete. It closely connects various hydration products of concrete to form a solid whole. Therefore, the quantity and distribution of C–S–H gel determine the mechanical strength of concrete materials.26,27 In this article, molecular dynamics analysis of C–S–H gels was carried out using Materials Studio simulation software to investigate the effects of temperature and humidity on the mechanical properties of 3D-printed concrete. First, Ca atoms, H2O molecules, OH groups, and Si3O10 groups were selected for the construction of amorphous cell C–S–H using the amorphous cell module. The density was set to 2.32 g/cm3. The specific ratios are listed in Table 2.

Table 2 Elemental Ratios of the C–S–H Amorphous Cell

basic unit	Ca	H2O	OH	Si3O10	
proportional number	9	8	6	2	

4.3.1.1 Modeling of Molecular Dynamics at Different Temperatures

Before the simulation calculation, the Forcite module was used to minimize the energy of the C–S–H gel model, and the most stable C–S–H gel configuration was obtained. The compass force field was selected for the calculation. The fastest descent method, conjugate gradient method, and Newton method were applied for optimization to obtain the energy minimization configuration. The molecular dynamics simulation was conducted with the optimized model as the initial configuration. NPT ensemble was selected for relaxation calculation, and the Nose–Hoover method was used for temperature control and pressure control. The pressure was set to 1 × 10–5 GPa, and the temperature was set to 275, 293, 315, and 333 K, respectively.

The total relaxation time amounted to 100 ps with a time step of 1 fs, resulting in a total of 1 × 105 simulation steps. The energy curves corresponding to the C–S–H structure at different temperatures were obtained at the end of the calculation, and the potential energy curves reached equilibrium after running for 15 ps, which indicated that the C–S–H gel structure reached a stable state. The optimized C–S–H model (Figure 8) was used to calculate the mechanical property parameters of the system.

Figure 8 C–S–H amorphous cell model construction process (at 21 °C for example).

Next, the CaO model was constructed. The Build Layers module was used to build the C–S–H/CaO interface model from CaO and C–S–H. The completed C–S–H/CaO model was constructed, as shown in Figure 9. The molecular dynamics relaxation process was carried out on this model, and the temperatures were likewise set at 275, 293, 315, and 333 K, respectively, to obtain the most stable configurations at different temperatures.

Figure 9 C–S–H/CaO modeling.

Figure 10 Different water-to-calcium ratios model of C–S–H: (a) H2O/Ca = 0.4, (b) H2O/Ca = 0.6, (c) H2O/Ca = 0.8, and (d) H2O/Ca = 0.98.

4.3.1.2 Modeling of Molecular Dynamics at Different Humidity Levels

The water-to-calcium ratio (H2O/Ca) was used to characterize the effect of environmental humidity on the materials in this paper. To further investigate the influence law of water molecules on the mechanical properties of the C–S–H gel model caused by environmental humidity, the C–S–H model with water-to-calcium ratios of 0.4, 0.6, 0.8, and 0.98 was set up for molecular dynamics analysis. The specific configuration is shown in Table 3.

Table 3 Number of Basic Units for Models with Different Water-to-Calcium Ratios

H2O/Ca	numbers of Ca	numbers of H2O	numbers of OH	numbers of Si3O10	numbers of total atoms	
0.4	90	36	60	20	578	
0.6	90	54	60	20	632	
0.8	90	72	60	20	686	
0.98	90	88	60	20	734	

The constructed C–S–H model at different water–calcium ratios is shown in Figure 10. The C–S–H/CaO models with different water-to-calcium ratios were constructed according to the steps in Section 4.3.1.1. Molecular dynamics relaxation was performed on the C–S–H and C–S–H/CaO models, respectively, to obtain the most stable configuration. The relaxation temperature was set at 293 K, and other parameters were set unchanged.

According to the relationship between the stress–strain and stiffness matrix of concrete, the Mechanical Properties option in the Forcite module was run to calculate the elastic modulus of the C–S–H and C–S–H/CaO models. Based on Hill’s method, the shear modulus (G) and bulk modulus (K) of the C–S–H system were calculated, and the elastic modulus (E) was solved by eq 1.1

4.3.2 Curing Conditions

Covering a full range of curing conditions from low to high temperatures in common construction environments to explore the impact of temperature on material properties. A variety of humidity curing strategies in engineering practice were simulated to evaluate the evolution law of humidity on material properties and to provide a scientific basis for the application of materials under different climatic conditions.

The prepared 3D-printed concrete specimens were equally divided into two groups; one group of specimens was placed at different ambient temperatures (RH: 95%): 2, 21, 42, and 60 °C, labeled Groups A1 to A5. The printing specimens were first temperature-cured according to the curing schedule shown in Table 4. The cooling specimens were then placed in a standard curing box for the specified time.

Table 4 Curing Schedule at Different Temperature

(RH: 98%)	standstill phase	warming phase	 	thermostatic phase	cooling phase	
2 °C	21 °C, 6 h	3 h	 	2 °C, 5 h	4 h	
21 °C	 	 	18 h	 	 	
42 °C	21 °C, 6 h	3 h	 	42 °C, 5 h	4 h	
60 °C	21 °C, 6 h	3 h	 	60 °C, 5 h	4 h	

Another group of specimen blocks were placed at different ambient humidity levels: air curing, film curing, watering curing, and standard curing. The air curing condition refers to the indoor environment of the laboratory. The film curing condition was defined as the covering of the specimen with film immediately after the specimen was removed from the mold without any manipulation of the concrete specimen before measurement. The watering curing condition referred to the watering of the concrete test blocks with a spray can in the morning and afternoon of each day after the test blocks were taken out of the molds with the spraying volume fixed at 10 mL. The standard curing condition referred to the placing of the test blocks in a standard curing box with the temperature and humidity values set at 21 ± 1 °C temperature and 95% relative humidity.

4.3.3 Mechanical Performance Test Methods

The printing size was 400 mm × 175 mm × 48 mm, and the thickness of the printed layer was 12 mm, with a total of four layers. The printing rate was 50 mm/s. The printed specimens were cured in the indoor environment for 24 h and then cut into 40 × 40 × 40 mm (for compressive strength test) and 40 × 40 × 160 mm (for flexural strength). The cut concrete specimen blocks were subjected to 1-, 3-, and 28-day strength tests. The direction of force was parallel to the direction of the print stacking. The testing schemes for flexural strength and compressive strength are shown in Figure 11.

Figure 11 Mechanical properties test of 3D-printed concrete.

The authors declare no competing financial interest.

Acknowledgments

The work was supported by the National Natural Science Foundation of China (grant number 52205338), the Natural Science Foundation of Liaoning Province (grant number 2023-BS-177), the Liaoning Province Department of Education Fund (grant number JYTMS20230438), the Open Foundation of Dalian Jinshiwan Laboratory (grant number Dljswkf202405), and Special Funds for Basic Research Operating Costs of Undergraduate Colleges and Universities in Liaoning Province (grant number LJBKY2024009).
==== Refs
References

Han Y. ; Yang Z. ; Ding T. ; Xiao J. Environmental and economic assessment on 3D printed buildings with recycled concrete. J. Cleaner Prod. 2021, 278 , 123884 10.1016/j.jclepro.2020.123884.
Singh N. ; Colangelo F. ; Farina I. Sustainable Non-Conventional Concrete 3D Printing—A Review. Sustainability 2023, 15 (13 ), 10121 10.3390/su151310121.
Khan S. A. ; Koç M. ; Al-Ghamdi S. G. Sustainability assessment, potentials and challenges of 3D printed concrete structures: A systematic review for built environmental applications. J. Cleaner Prod. 2021, 303 , 127027 10.1016/j.jclepro.2021.127027.
Chen Y. ; Chaves Figueiredo S. ; Yalçinkaya Ç. ; Çopuroğlu O. ; Veer F. ; Schlangen E. The Effect of Viscosity-Modifying Admixture on the Extrudability of Limestone and Calcined Clay-Based Cementitious Material for Extrusion-Based 3D Concrete Printing. Materials 2019, 12 (9 ), 1374 10.3390/ma12091374.31035317
Samudrala M. ; Mujeeb S. ; Lanjewar B. A. ; Chippagiri R. ; Kamath M. ; Ralegaonkar R. V. 3D-Printable Concrete for Energy-Efficient Buildings. Energies 2023, 16 (10 ), 4234 10.3390/en16104234.
Sun Y. ; Li G. ; Zhang J. ; Sun J. ; Xu J. ; Qiusong C. ; Chen Q. Development of an Ensemble Intelligent Model for Assessing the Strength of Cemented Paste Backfill. Adv. Civ. Eng. 2020, 2020 , 1643529 10.1155/2020/1643529.
Sai S. L. ; Kasagani H. ; Sri Ram Ravi Teja P. ; Uday Kiran Naik M. ; Jithendra M. P. D. Experimental Investigation on Thermal Insulation of Sustainable 3D Printable Concrete by Using Corncob Powder. IOP Conf. Ser.: Mater. Sci. Eng. 2023, 1280 (1 ), 012013 10.1088/1755-1315/1280/1/012013.
Olawumi M. A. ; Oladapo B. I. ; Ikumapayi O. M. ; Akinyoola J. O. Waste to wonder to explore possibilities with recycled materials in 3D printing. Sci. Total Environ. 2023, 905 , 167109 10.1016/j.scitotenv.2023.167109.37717760
Sathiparan N. ; Jeyananthan P. Soft computing techniques to predict the compressive strength of groundnut shell ash-blended concrete. J. Eng. Appl. Sci. 2023, 70 (1 ), 134 10.1186/s44147-023-00302-9.
Colyn M. ; van Zijl G. ; Babafemi A. J. Fresh and strength properties of 3D printable concrete mixtures utilising a high volume of sustainable alternative binders. Constr. Build. Mater. 2024, 419 , 135474 10.1016/j.conbuildmat.2024.135474.
Du J. ; Wei Y. ; Zhang H. ; Idriss A. I. B. Effects of oyster shell derivatives on performance enhancement of biomass-based 3D printed concrete. Mater. Res. Express 2024, 11 (6 ), 065504 10.1088/2053-1591/ad5646.
Xiao J. ; Han N. ; Zhang L. ; Zou S. Mechanical and microstructural evolution of 3D printed concrete with polyethylene fiber and recycled sand at elevated temperatures. Constr. Build. Mater. 2021, 293 , 123524 10.1016/j.conbuildmat.2021.123524.
Zou P. ; Chang H. ; Wang F. ; Cai Y. ; Zhang Z. ; Zhao Z. ; Lv Z. Effect of steam curing scheme on the early-age temperature field of a prefabricated concrete T-beam. Case Stud. Constr. Mater. 2024, 20 , e02787 10.1016/j.cscm.2023.e02787.
Wei X. ; Ming F. ; Li D. ; Chen L. ; Liu Y. Influence of Water Content on Mechanical Strength and Microstructure of Alkali-Activated Fly Ash/GGBFS Mortars Cured at Cold and Polar Regions. Materials 2019, 13 (1 ), 138 10.3390/ma13010138.31905783
Miao Y. ; Lu Z. ; Wang F. ; Wang H. ; Li Y. ; Lin J. ; Jiang J. Shrinkage cracking evolvement in concrete cured under low relative humidity and its relationship with mechanical development. J. Build. Eng. 2023, 72 , 106670 10.1016/j.jobe.2023.106670.
Shahmirzadi M. R. ; Gholampour A. ; Kashani A. ; Ngo T. D. Shrinkage behavior of cementitious 3D printing materials: Effect of temperature and relative humidity. Cem. Concr. Compos. 2021, 124 , 104238 10.1016/j.cemconcomp.2021.104238.
Wang B. ; Yao X. ; Yang M. ; Zhang R. ; Huang J. ; Wang X. ; Dong Z. ; Zhao H. Mechanical Performance of 3D Printed Concrete in Steam Curing Conditions. Materials 2022, 15 (8 ), 2864 10.3390/ma15082864.35454556
Yao X. ; Lyu X. ; Sun J. ; Wang B. ; Wang Y. ; Yang M. ; Wei Y. ; Elchalakani M. ; Li D. ; Wang X. AI-based performance prediction for 3D-printed concrete considering anisotropy and steam curing condition. Constr. Build. Mater. 2023, 375 , 130898 10.1016/j.conbuildmat.2023.130898.
Liu P. ; Chen Y. ; Yu Z. Effects of temperature, relative humidity and carbon dioxide concentration on concrete carbonation. Mag. Concr. Res. 2020, 72 (18 ), 936–947. 10.1680/jmacr.18.00496.
Liu D. ; Zhang Z. ; Zhang X. ; Chen Z. 3D printing concrete structures: State of the art, challenges, and opportunities. Constr. Build. Mater. 2023, 405 , 133364 10.1016/j.conbuildmat.2023.133364.
Zeyad A. M. ; Tayeh B. A. ; Adesina A. ; de Azevedo A. R. G. ; Amin M. ; Hadzima-Nyarko M. ; Saad Agwa I. Review on effect of steam curing on behavior of concrete. Cleaner Mater. 2022, 3 , 100042 10.1016/j.clema.2022.100042.
Wang L. ; Li Q. ; Hu Y. ; Cui T. ; Li R. Shrinkage and Cracking Properties of Cellulose Fiber–Concrete Composites for 3D Printing by Leveraging Internal Curing. Addit. Manuf. 2024, 11 (1 ), 50–59. 10.1089/3dp.2021.0281.
Bahraq A. A. ; Al-Osta M. A. ; Baghabra Al-Amoudi O. S. ; Obot I. B. ; Maslehuddin M. ; Ahmed H. ; Saleh T. A. Molecular Simulation of Cement-Based Materials and Their Properties. Engineering 2022, 15 , 165–178. 10.1016/j.eng.2021.06.023.
He J. ; Arab A. ; Zhang C. Molecular dynamics study of temperature and defects on mechanical properties of Gr(GO)/C-S-H composites. J. Non-Cryst. Solids 2024, 639 , 123094 10.1016/j.jnoncrysol.2024.123094.
Luo Q. ; Xie Y. ; Nie Q. ; Yang Q. ; Zhang X. Impact of pore sizes and defects on C-S-H/epoxy bonding in wet conditions: A molecular dynamics analysis. Next Materials 2024, 5 , 100253 10.1016/j.nxmate.2024.100253.
Geng Z. ; Tang S. ; Wang Y. A. H. ; He Z. ; He Z. ; Wu K. ; Wang L. Stress relaxation properties of calcium silicate hydrate: a molecular dynamics study. J. Zhejiang Univ., Sci., A 2024, 25 (2 ), 97–115. 10.1631/jzus.A2300476.
Jin S. ; Li J. ; Xu W. ; Ding Q. Heterogeneous Nature of Calcium Silicate Hydrate (C-S-H) Gel: A Molecular Dynamics Study. J. Wuhan Univ. Technol., Mater. Sci. Ed. 2020, 35 (2 ), 435–440. 10.1007/s11595-020-2275-8.
