# Printability Assessment of Cement-Based Materials Using Uniaxial Compression Test

Ilhame Harbouz, Ammar Yahia, Emmanuel Rozière, Ahmed Loukili

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Ilhame Harbouz, Ammar Yahia, Emmanuel Rozière, Ahmed Loukili. Printability Assessment of Cement-Based Materials Using Uniaxial Compression Test. Third RILEM International Conference on Concrete and Digital Fabrication, Jun 2022, Loughborough, United Kingdom. pp.318-323, 10.1007/978-3-031-06116-5_47. hal-04733423

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Submitted on 25 Dec 2025

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# Printability Assessment of Cement-Based Materials Using Uniaxial Compression Test

Ilhame Harbouz<fnref n="1" />,<fnref n="2" />✉, Ammar Yahia<fnref n="1" />, Emmanuel Rozière<fnref n="2" />, and Ahmed Loukili<fnref n="2" />

**Abstract.** Concrete 3D printing, a cutting-edge manufacturing technology, is grasping increasing interest in the construction industry. Striking a balance between extrudability and buildability of printable cement-based materials is crucial to ensure successful printing. Although rheology is widely used to assess flow properties, it can bring several challenges when assessing flow properties of stiff materials used in 3D printing, including wall slippage, liquid phase migration, jamming, shear localization, and aging. Moreover, in 3D printing applications, cement-based materials are usually subjected to compressive loads due to the weight of the printed layers. The uniaxial compression test is used to assess the printability of cement-based materials investigated in this study. Both the extrudability and buildability aspects have been discussed. Various mortar mixtures were proportioned using compatible chemical-admixture systems and different sand-to-cement ratios. The effect of the latter designing parameters on the printability of cement-based materials was evaluated. On the other hand, special attention was given to the stress-strain behavior of the investigated mixtures.

**Keywords:** Uniaxial compression test · Extrudability · Buildability · 3D printing · Cement-based materials

## 1 Introduction

The design of printable cement-based materials aims to meet specific performance criteria. At early age, fresh material should satisfy rheological requirements to achieve an optimum balance between its extrudability and shape stability [1]. The absence of the formwork requires the use of material with sufficient rigidity to support the weight of the successive printed layers. Stiff materials are therefore the most commonly used in 3D printing applications. It is generally difficult to characterize the rheology of this type of material using rotational rheometers. The uniaxial compression test is an alternative method to determine the flow behaviour of highly concentrated and stiff suspensions [2–4]. This method overcomes the common problems of conventional rheometry, such as slip, plastic material disruption, shear banding, and the difficulty of loading stiff materials in rotational devices.

The uniaxial compression test can characterize cement-based materials by compressing a cylindrical specimen between two parallel surfaces with a controlled force. In the

<footnote n="1">¹ Université de Sherbrooke, Sherbrooke, Québec J1K 2R1, Canada
ilhame.harbouz@USherbrooke.ca</footnote>

<footnote n="2">² Nantes Université, Ecole Centrale Nantes, CNRS, GeM, UMR 6183, 44000 Nantes, France</footnote>
present study, this test is used to evaluate the extrudability of printable materials according to the recommendations reported by Toutou et al. [2, 3]. On the other hand, the buildability aspect is assessed through the elastic response of the investigated materials. The influence of viscosity-modifying agent and sand-to-cement ratio on stress-strain behavior and its time evolution is discussed.

# 2 Materials and Methods

## 2.1 Materials

Four mortar mixtures were proportioned using general use (GU) Portland cement and fine graded quartz sand with a maximum aggregate size of 0.7 mm and a specific gravity of 2.66. A polycarboxylate-ether based high-range water reducer (PCE-based HRWR) with a specific gravity of 1.09 was used. The investigated mortar mixtures were proportioned with different sand-to-cement ratios (S/C) and HRWR dosages to achieve an initial spread flow of $152.5 \pm 2.5$ mm. On the other hand, a viscosity-modifying agent (VMA) was employed to evaluate its effect on the stress-strain of printable mortar behavior. The mixture proportions of the investigated mixtures are summarized in Table 1.

<table><caption>**Table 1.** Mixture proportions of the investigated mixtures</caption><thead><tr><th></th><th>Sand</th><th>Cement</th><th>Water</th><th>E/C</th><th>S/C</th><th>SP (%woc)</th><th>VMA (%woc)</th></tr></thead><tbody><tr><td>M1</td><td>465.3</td><td>930.6</td><td>325.7</td><td>0.35</td><td>1.0</td><td>0.02%</td><td>—</td></tr><tr><td>M1 - T</td><td>465.3</td><td>930.6</td><td>325.7</td><td></td><td>1.0</td><td>0.04%</td><td>0.05%</td></tr><tr><td>M2</td><td>533.0</td><td>852.7</td><td>298.5</td><td></td><td>1.25</td><td>0.20%</td><td>—</td></tr><tr><td>M3</td><td>568.4</td><td>812.0</td><td>284.2</td><td></td><td>1.4</td><td>0.25%</td><td>—</td></tr></tbody></table>

## 2.2 Mixing Sequence and Test Procedures

The investigated mixtures were prepared using a planetary Hobart mixer. Dry ingredients were first mixed for 1 min at the lowest mixing speed. The water along with HRWR were added and mixed at the same velocity for 3 min, and then the viscosity modifying agent was added (if applicable). Finally, the edges of the bowl were scraped, and a higher mixing speed was applied for 2 additional minutes to ensure a homogeneous mixture. Cylindrical samples of 20 mm height (h) and 40 mm radius (R) were then molded, as shown in Fig. 1.

The uniaxial compression test was conducted to evaluate the extrudability and buildability of the investigated mixtures, based on their stress-strain behavior. The uniaxial compression test plate has an equal radius of 40 mm of the sample. The mortar samples were squeezed out between two parallel discs. The upper disc was displaced at a constant velocity of 1 kPa/s, simulating the successive layers casting in 3D printing, while the
lower one is maintained stationary. It is worth mentioning that the tested sample per-
manently fills the area between the plates, hence ensuring a constant compressed area.
The normal force was recorded as a function of time and the gap between the plates was
measured using an LVDT strain gauge. The uniaxial compression test measurements
were performed at 10 min and 1 h after mixing. All uniaxial compression experiments
were repeated three times to ensure the repeatability of the results.

<figure><img src="image_2.png" /><figcaption>**Fig. 1.** (Right) The uniaxial compression device and (left) the samples preparation using custom-made molds (*Credits to Moeini* [5])</figcaption></figure>

The extrudability of the investigated mixtures was evaluated by considering the variation of the reduced compression load (F* = -Fh/πR³) with the geometrical ratio (h/R) [2, 3]. As can be observed in Fig. 2, the typical response curve can be divided into three different phases. The first phase corresponds to the initial elastic compaction response, where the mortar exhibits some elasticity and would compact before any noticeable flow occurs. A transitional plastic phase where flow takes place is observed, followed by a consolidation phase depicted at the end, which is characterized by a decrease in the deformation rate due to the liquid-phase migration phenomenon [6].

The plastic yield value Kᵢ defined in [3] was determined using the regression line within the plastic response domain of the test results. Only the reduced compression force value for h/R = 0 was considered due to the influence of the radial traction stress around the sample [3]. This parameter will be used to evaluate the extrudability of the investigated mortars, as proposed by [2]. The corresponding limited loads and stains of the transitional plastic domain were identified to compare the elastic and plastic responses of the investigated mixtures, and are denoted respectively by (σel, εel) and (σpl, εpl). The evolution of these parameters over time was used to assess the buildability of the investigated mixtures.

**3 Results and Discussions**

The results of the uniaxial compression test of the investigated mortar mixtures are
presented in Fig. 3a. The squeeze test parameters defined in the previous section are
summarised in Table 2. The obtained results showed that mixtures with higher flowability
exhibited the first transition at lower strain values and the particle’s phase migration at
higher strain, as observed with the mixture M1 (Fig. 3a). This can be due to the relatively
<figure><img src="image_3.png" /><figcaption>**Fig. 2.** Typical response curve of the uniaxial compression test</figcaption></figure>

low solid volume and the presence of PCE-based HRWR, hence leading to a weak percolated network. On the other hand, the plastic response observed with M1-T, M2, and M3 mixtures was obtained only for short ranges of h/R values. Besides, the increase in the sand-to-cement ratio resulted in reducing the plastic response. This is mainly attributed to the frictional effect of sand particles to withstand the plastic squeezing flow, hence leading to higher $K_i$. This resulted in very high shape retention of the mixtures under high loading values, as shown in Fig. 3a. Referring to the extrudability criteria reported in literature [2, 7], the investigated mixtures seem to be within the extrudability ranges, except for the M1 mixture that exhibited a $K_i$ value lower than 20 kPa, which may have a low shape retention after extrusion. On the other hand, the M3 mixture may require a relatively higher extrusion pressure due to its high $K_i$ value. It can therefore be assumed that extrudable mixtures should be designed to achieve $K_i$ value high enough ($K_i$ > 20 kPa) to ensure good shape stability, but sufficiently low than the maximum pressure that can be set by the extrusion device.

The M1-T mixture incorporating a viscosity modifying agent exhibited higher elastic and plastic strengths (54.88 kPa, 81.94 kPa), and lower strain values compared to M1 mixture (27.32 kPa, 32.72 kPa). This increased the elastic modulus $E_{el}$ of the mortar sample, which implies high strength-based stability of the mixture during the printing process [1]. On the other hand, the deformation rate in the consolidation phase remained unchanged compared to M1 mixture, whereas the increase in the sand-to-cement ratio greatly increased the consolidation rate of the mixture. The addition of the VMA can therefore be useful to improve the buildability of flowable materials for free deposition printing applications.

As can be observed in Fig. 3b, at higher ages, the transitional plastic phase is hardly identified. At later age, the mixtures undergo monotonic (i.e. no transitional phases) behavior under compressional load [5]. This can be due to the flow loss of the mixtures. Hence, tracking the shift between these two responses can be useful to study the fluid-solid transition behavior in 3D printing applications. The increase in the S/C ratio greatly
<table><caption>**Table 2.** Squeeze test parameters of the investigated mortar mixtures</caption><thead><tr><th></th><th>Ki (kPa)</th><th>σ<sub>el</sub> (kPa)</th><th>ε<sub>el</sub> (-)</th><th>E<sub>el</sub> (kPa)</th><th>σ<sub>pl</sub> (kPa)</th><th>ε<sub>pl</sub> (-)</th></tr></thead><tbody><tr><td colspan="7"><strong>t = 10 min</strong></td></tr><tr><td>M1</td><td><strong>16.20</strong></td><td>27.3</td><td>0.326</td><td><strong>83.8</strong></td><td>32.7</td><td>0.820</td></tr><tr><td>M1-T</td><td><strong>119.19</strong></td><td>54.9</td><td>0.269</td><td><strong>204.4</strong></td><td>81.9</td><td>0.452</td></tr><tr><td>M2</td><td><strong>131.16</strong></td><td>29.2</td><td>0.253</td><td><strong>115.6</strong></td><td>79.9</td><td>0.434</td></tr><tr><td>M3</td><td><strong>213.90</strong></td><td>35.7</td><td>0.246</td><td><strong>145.0</strong></td><td>112.0</td><td>0.424</td></tr><tr><td colspan="7"><strong>t = 60 min</strong></td></tr><tr><td>M1</td><td><strong>424.11</strong></td><td>47.3</td><td>0.185</td><td><strong>256.2</strong></td><td>250.4</td><td>0.506</td></tr><tr><td>M1-T</td><td>-</td><td>100.4</td><td>0.151</td><td><strong>665.2</strong></td><td>-</td><td>-</td></tr><tr><td>M2</td><td>-</td><td>110.8</td><td>0.142</td><td><strong>780.3</strong></td><td>-</td><td>-</td></tr><tr><td>M3</td><td>-</td><td>131.3</td><td>0.120</td><td><strong>1094.2</strong></td><td>-</td><td>-</td></tr></tbody></table>

increased the rate of evolution of the Elastic modulus (E<sub>el</sub>), as observed with the M2 and M3 mixtures. This improves the buildability of the mortars, but it increases the risk of workability loss. On the other hand, the addition of VMA increased the elastic strength σ<sub>el</sub> with time. This highlights the importance of incorporating VMA in 3D printing applications.

<figure><img src="image_4.png" /><figcaption>**Fig. 3.** (a) Uniaxial compression test results (b) Time evolution response of M1 and M3 mixtures</figcaption></figure>

## 4 Conclusions

The uniaxial compression test was found to be an effective tool to assess the printability of cement-based materials. This method can be useful for optimizing the mixture design adapted for 3D printing applications. The incorporation of viscosity modifying agents
(VMA) was useful in ensuring printability requirements of flowable materials. On the other hand, the increase in the sand-to-cement ratio enhanced both the elastic and plastic strengths, as well as the strain-hardening rate, which may cause clogging problems. The plastic yield value $K_i$ allowed comparing the extrudability of the investigated mixtures regarding their shape retention and extrusion pressure. The buildability aspect of the investigated mixtures was assessed through their elastic response. The compression loading increment can simulate the multilayer casting rate in the printing process. A transition response was observed after 1 h of age, which is characterized by the absence of the plastic phase. A detailed study should be conducted to understand the microstructural changes during this transition phase.

## References

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2. Toutou, Z., Roussel, N., Lanos, C.: The squeezing test: a tool to identify firm cement-based material's rheological behaviour and evaluate their extrusion ability. Cem. Concr. Res. **35**(10), 1891–1899 (2005). https://doi.org/10.1016/j.cemconres.2004.09.007

3. Roussel, N., Lanos, C.: Plastic fluid flow parameters identification using a simple squeezing test. Appl. Rheol. **13**(3), 132–141 (2003). https://doi.org/10.1515/arh-2003-0009

4. Estellé, P., Lanos, C., Mélinge, Y., Servais, C.: Squeezing flow for rheological characterisation of food materials. In: 3rd International Symposium on Food Rheology and Structure (ISFRS 2003), Zurich, Switzerland, pp. 115–119, February 2003. https://hal.archives-ouvertes.fr/hal-00664501. Accessed 30 Jan 2022

5. Moeini, M.A.: Rheology of cement-based materials used for large-scale 3D printing. https://savoirs.usherbrooke.ca/bitstream/handle/11143/18774/moeini_mohammad_amin_PhD_2021.pdf?sequence=10&isAllowed=y. Accessed 30 Jan 2022

6. Mascia, S., Patel, M.J., Rough, S.L., Martin, P.J., Wilson, D.I.: Liquid phase migration in the extrusion and squeezing of microcrystalline cellulose pastes. Eur. J. Pharm. Sci. **29**(1), 22–34 (2006). https://doi.org/10.1016/j.ejps.2006.04.011

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