# Experimental Study on Foci Development in Mortar Using Seawater and Sand

^{1}

^{2}

^{3}

^{4}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Composition of the Mortar

^{th}, 2016 and the quantitative fabric experiment lasted from a.m. 10:30 to p.m. 17:50 on Dec 10

^{th}, 2016. The quantitative fabric of the seawater specimen, including the key ions and the saline minerals, is shown in Figure 2.

^{−3}‰ and the descending sequence of the others was Cl

^{−}with 13768.18 × 10

^{−3}‰, Na

^{+}with 7076 × 10

^{−3}‰, MgCl

_{2}with 3574.38 × 10

^{−3}‰, CaSO

_{4}with 1074.74 × 10

^{−3}‰, Mg

^{2+}with 903 × 10

^{−3}‰, SO

_{4}

^{2−}with 780 × 10

^{−3}‰, K

_{2}SO

_{4}with 607.66 × 10

^{−3}‰, Ca

^{2+}with 316.1 × 10

^{−3}‰, K

^{+}with 272.4 × 10

^{−3}‰, and Br

^{−}with 40 × 10

^{−3}‰.

^{−}

^{5}mm ~ 2mm), and the results are offered in Figure 3. Equations (1) and (2) define the characteristic parameters of the sea sand particles, i.e., the uniformity coefficient C

_{u}and the curvature coefficient C

_{c}[21], and their expectation values from the statistical work are reported in Table 3. Moreover, C

_{u}and C

_{c}help to evaluate the uniformity and the continuousness of powder materials, inclusive of the sea sand, respectively.

_{10}, d

_{30}, d

_{50}, and d

_{60}here designate the specific particle sizes with their cumulative composition percentages as 10%, 30%, 50%, and 60%, respectively.

_{u}with the value beyond 5 indicates that the material particles have the non-uniform distribution. C

_{u}with the value below 5, by contrast, means that the material particles have uniform distribution. With regard to continuousness, C

_{c}with the span (1, 3) shows the continuous distribution of the material particles. Otherwise, some intermediate size groups have been lost. Hence, the sea sand of Nansha shore had the uniform and discontinuous distribution.

_{2}base and the original micro-cracks were covered by KAlSi

_{3}O

_{8}texture and Na(Si

_{3}Al)O

_{8}chips. The irregular surface of the sea sand helped to strengthen the connection between the material particle and the hydrate gel. Surely, the chip cover played X factor on the micro-interfacial behavior of the mortar using seawater and sand. Hence, the micro-interfacial behavior of the sea sand and the hydrate gel should be specifically ascertained.

_{2}SiO

_{4}, Ca

_{3}SiO

_{5}, Ca

_{3}Al

_{2}O

_{6}, SiO

_{2}, Al

_{2}O

_{3}, CaO, and MgO.

#### 2.2. Experiments’ Standards, Equipments and Methods

^{3}, respectively. Meantime, the principal stress ${\sigma}_{2}$ was produced in the mortar specimen in the same direction of the confining load.

_{i}on the strain and stress curve was the corresponding position of MSHCT scan of the ith time and n was the total of MSHCT scan (n = 6 in this study). $\epsilon $ and $\sigma $ represented the SSS of the mortar. ${\sigma}_{{}_{1}}^{\left(i\right)}$ and ${\sigma}_{{}_{2}}^{\left(i\right)}$ designated the principal stress states of the ith time. Particularly, the strain and stress states (i.e., SSS) that could quantified the damage mathematically and the MSHCT images that could quantified the damage graphically were synchronically collected by the help of the tri-axial CT scanner system.

## 3. Results and Discussion

^{st}, 2

^{nd}, and 3

^{rd}curves interpreted the relations of the strain states on the principal stress ${\sigma}_{1}$. Moreover, the cyan rectangles on the three curves of Figure 11 represented the positions of MSHCT scan. The sequence of the positions of MSHCT scan was prescribed by the serial number T

_{i}(i = 1~6) and the blue arrows along the 1

^{st}, 2

^{nd}, and 3

^{rd}curves. Meantime, six marginal points were specified on the three curves of Figure 11, namely, A, B, C, D, E, and F, that, indicated by the pink circles, helped to define the critical states of the physical-chemical-mechanical performance of the mortar specimen.

_{1}, T

_{2}, T

_{3}, T

_{4}, T

_{5}, and T

_{6}. Meanwhile, the foci development were correspondingly detected, measured, and reconstructed in six MSHCT scan positions.

**Interval 0-A on the curves in Figure 11:**The value of ${\epsilon}_{\mathrm{a}}$ in the direction of the axial load ${\sigma}_{\mathrm{a}}$ was 0 at point A, where the driving shaft (i.e., the vertical main-shaft) under the parking state had no motion and the axial load has not been worked. The confining load of 2 MPa (i.e., ${\sigma}_{\mathrm{c}}$ = 2 MPa), by contrast, has been worked on the normal cylinder specimen at the same time in order to stabilize the radial stress state, which demonstrated the storage environment of the material. The priority of the confining load has been accepted by most tri-axial experiments, because it can simulate the original storage environments of the studied materials. The undisturbed performance of the studied materials in the host could thereby be recovered during the tri-axial experiments. Hence, this procedure was defined as stress maintenance. Consequently, the volumetrically contractive strain at point A was 5.09 × 10

^{−5}, which was produced by the radial deformation, the value of the radially compressive strain of which was −2.59 × 10

^{−5}. Furthermore, the volumetrically contractive strain of interval 0-A showed the linearity of the mortar specimen. Meanwhile, the original state of the mortar specimen ((a) in Figure 12) expressed that the temporary compression of the parental focus contributed to the linearly volumetric contraction.

**Interval A-B on the curves in Figure 11:**The radial strain ${\epsilon}_{\mathrm{r}}$ value of interval A-B (including point A) in the direction of ${\sigma}_{\mathrm{c}}$ was the minus one, which indicated that the radius of the mortar specimen has been compressed to be the shorter one. −2.17 × 10

^{−5}was the value of the radially compressive strain of point B on 3

^{rd}curve of Figure 11. The maximally absolute value of the minus radial strain at interval A-B was 1.38 × 10

^{−4}. Meanwhile, the axial strain that was produced by the axially compressive deformation accumulated up to 1.96 × 10

^{−3}(at point B on 1

^{st}curve of Figure 11) and the maximally volumetric strain of interval A-B attained 1.99 × 10

^{−3}(at point B on 2

^{nd}curve of Figure 11). Hence, it can be deduced that the totally volumetric deformation here was the contractive one, in both the axial direction and radial direction. However, the minus radial strain with the maximally absolute value and the maximally volumetric strain did not arise at the same time at interval A-B. The maximally volumetric strain lagged behind the minus radial strain, with the maximally absolute value at interval A-B. Furthermore, the development of the axial strain and the volumetric one significantly showed the linear and the non-linear characteristics, respectively. Meanwhile, the radial strain here also developed non-linearly. Consequently, the non-linearly radial strain has caused the non-linearity of the volumetric strain, the contribution to which was the micro-cavities’ compaction in Figure 13. The gel-like constituents around the micro-cavities (including C-S-H and Friedel’s salt) were locked in the radial direction, which created the non-linearly radial strain. Meantime, Figure 13 showed that both the volumetric strain and radial strain were the contractive ones and the C-S-H contraction helped to imprison the local Friedel’s salt. Thereby, the dispersion of Friedel’s salt was impeded.

**Interval B-C on the curves in Figure 11:**In terms of the direction of ${\sigma}_{1}$(i.e., the direction of the axial load ${\sigma}_{\mathrm{a}}$), the peak strength of the mortar using seawater and sand was 33.88 MPa, indicated by point C on the three curves in Figure 11. The values of ${\epsilon}_{\mathrm{a}}$ and ${\epsilon}_{\mathrm{v}}$ at point C were 1.23 × 10

^{−2}and 1.0 × 10

^{−2}, respectively. Correspondingly, they accounted for 62.11% and 95.61% of the peak values of ${\epsilon}_{\mathrm{a}}$ and ${\epsilon}_{\mathrm{v}}$ (denoted by point D on the 1

^{st}and 2

^{nd}curves in Figure 11). Meantime, the radial strain at point C in the 3

^{rd}curve was 1.09 × 10

^{−3}. Particularly, the axial strain of the interval B-C was produced by the compressive deformation in the direction of ${\sigma}_{1}$. On the contrary, the radial strain here was produced by the tensile deformation in the direction of ${\sigma}_{\mathrm{c}}$. Moreover, the volumetric strain of the interval B-C has been generated by the global contraction of the normal cylinder specimen. Therefore, the conclusions that are deduced from the characteristics of the interval B-C included that the development of the peak strength would consume more than half of the axially compressive strain and most of the volumetrically contractive strain; however, the radial strain with the soft loading condition was under-developed when the mortar reached its peak strength in the ${\sigma}_{1}$ direction; the radial strain here, at the same time, indicated the absolutely tensile deformation in the ${\sigma}_{\mathrm{c}}$ direction; hence, the axial compression has dwarfed the radial extension and resultantly generated the global contraction of the normal cylinder specimen. Meanwhile, the MSHCT state of the mortar specimen ((b) in Figure 12) showed that the distribution of the cohesive continuum around the parental focus has been explicitly disturbed and the promising damage zones have been fused to be a connectively larger area in the core of which the outline of the parental focus was squeezed to be a smooth configuration. Moreover, a new baby focus was generated at the 12 o’clock direction of the parental one in position T

_{3}. The distance between the parental focus and the new baby one was 11.31mm and their connective region was destroyed to be the macro-fragments ((c) in Figure 12). The maximal size of the macro-fragments reached 4 mm at interval B-C.

**Interval C-D on the curves in Figure 11:**${\epsilon}_{\mathrm{a}}$ and ${\epsilon}_{\mathrm{v}}$ reached their peak values (as indicated by point D on the 1

^{st}and 2

^{nd}curves) at the same stress state where ${\sigma}_{1}$ = 20.34 MPa at the backbone of the hysteresis loop in Figure 11. The peak values of ${\epsilon}_{\mathrm{a}}$ and ${\epsilon}_{\mathrm{v}}$ were 1.61 × 10

^{−2}and 1.14 × 10

^{−2}, respectively. Meantime, the mortar strength began to drop steeply after the peak value (represented by point C on the three curves in Figure 11) towards the strain coordinate axis. On the other side, the axially compressive strain of interval C-D still increased along the negative direction of the ${\sigma}_{1}$ coordinate axis. Similarly, the radial strain here that was caused by the tensile deformation showed the reversely climbing trend when compared with the radial strain development of interval B-C. In contrast, in the position T

_{5}of 2

^{nd}curve, a locally odd fall lived, which indicated the relatively dilative deformation. Furthermore, the locally high-angle zones happened directly in position 6 of both the axial strain curve and the radial strain one (namely, the 1

^{st}and 3

^{rd}curves in Figure 11). Especially, the locally odd fall on the 2

^{nd}curve triggered the fluctuation of the volumetric strain around it, which denoted the alternate deformations of the volumetric contraction and dilation. The maximal values of the contractive strain and the dilative one of volumetric deformation here were 1.03 × 10

^{−}

^{2}and 4.02 × 10

^{−4}, respectively. Therefore, it can be confirmed that the local fractures that presented the abruptly volumetric deformation have burst in the normal cylinder specimen ((d) in Figure 12); the locally steep rise of the radially tensile strain defeated the development of the axially compressive strain, which created the relatively dilative deformation of the mortar (position T

_{5}of 2

^{nd}curve and (e) in Figure 12). The local fracture that caused the abrupt volumetric dilation was built by three zones, namely: the interface failure zone, where the sea sand particle was pulled half out of the hydrate layers and the framework of the mortar was collapsed; the crack zone, where the hydrate layers, including mainly C-S-H, C-A-S-H, and N-A-S-H gel were partially broken into a volumetric crack; and, the breakage zone, where the needle-like AFt (namely, ettringite) was snapped and its clastic ones clogged and enlarged the volumetric crack with the coupled effects of its growth and the load accumulation (Figure 14).

**Interval D-E on the curves in Figure 11:**The axial strain ${\epsilon}_{\mathrm{a}}$ began to drop after the peak value 1.61 × 10

^{−2}at point D of the 1

^{st}curve in Figure 11. The principal stress ${\sigma}_{1}$ at point E of the three curves in Figure 11 was 13.53 MPa, with the correspondingly axial strain 1.5 × 10

^{−2}, where the framework of the normal cylinder specimen began to crumble due to the re-adjustment of ${\epsilon}_{\mathrm{a}}$ development. Particularly, the re-adjustment of ${\epsilon}_{\mathrm{a}}$ development produced the loose connection among the macro-fragments and undermined the mortar strength. Meanwhile, the smart extensometer of the tri-axial sub-system decelerated tracing the axial deformation to prohibit the possible injury against the sub-system. The driving shaft then started to gradually rest here. Hence, coupled with the strength reduction, the dropping trend of the axially compressive strain represented that the axially tensile deformation was marginally recovered as a result of the gradual rest of the vertical main-shaft, which helped to partially retrieve the elasticity of the mortar. Moreover, the confining load here failed to effectively confine the radially tensile deformation due to the crumbled framework of the normal cylinder specimen. The maximal gradient of the radial tensile strain with the axial load (i.e., ${\epsilon}_{\mathrm{r}}$/${\sigma}_{\mathrm{a}}$) resided at interval D-E and the value was 4.03 × 10

^{−4}/MPa that indicated the relatively volumetric dilation of the mortar. The 2

^{nd}curve in Figure 11 showed that the maximal value of the relatively volumetric dilative strain at interval D-E was 4.94 × 10

^{−3}, which denoted that the confining load could not resist the volumetric dilation in radial direction again. Particularly, the partially retrieved elasticity in the axial direction also contributed to the relatively volumetric dilation of the mortar the framework of which has been radically re-organized during the elastic recovery.

**Interval E-F on the curves in Figure 11:**The mortar strength was softened by the penetrating cracks ((f) in Figure 12) at interval E-F and its framework absolutely collapsed due to the widespread microscopic deterioration in Figure 15.

^{rd}curve in Figure 11), the re-increment of the axial strain (1

^{st}curve in Figure 11) indicated that the volumetric dilation of the mortar was out of control, with which, the resilient performance of the axial load caused the absolute collapse of the framework instead of the strength retrieve. The residually axial load ${\sigma}_{\mathrm{a}}$ in the position F was 13.64 MPa. Correspondingly, the axial strain ${\epsilon}_{\mathrm{a}}$, the volumetric strain ${\epsilon}_{\mathrm{v}}$, and the radial one ${\epsilon}_{\mathrm{r}}$ here were 1.52 × 10

^{−2}, 5.19 × 10

^{−3}, and 4.95 × 10

^{−3}, respectively. Moreover, the residual strength could help prevent sharp destruction of engineering bodies that are composed with the mortar using seawater and sand.

## 4. Conclusions

- The main source of the saline minerals in the mortar was the seawater used for the specimens’ preparation. The saline minerals were partly dissipated as a result of the curing treatment. However, the residual saline minerals generated the micro-interfacial flaws coupled with the uniform and discontinuous distribution of the sea sand particles.
- The local fracture could be controlled by the active adjustment for the distribution of the sea sand. The bigger sea sand particles could strengthen the framework of the mortar and the smaller ones played the key role in residual saline minerals’ absorption.
- The micro-interfacial behavior of the sea sand and the hydrate gel partially controlled the performance of the mortar. The factors inclusive of the curing, the surface pattern of the sea sand, and the gel type crucially worked on the micro-interfacial behavior, which should be specifically studied.
- The principal constituents of the composite Portland cement P.C 42.5 R included Ca
_{2}SiO_{4}, Ca_{3}SiO_{5}, and Ca_{3}Al_{2}O_{6}that contributed to the hydrate generation of the mortar using seawater and sand. - The cause why the on-line damage detection experiments art was designed is that the art helps to quantify the foci development by the visualized measurement of the damage.
- According to the results from the on-line damage detection experiments, the priority of the confining load produced the linearly volumetric contraction due to the temporary compaction of the parental foci in the mortar specimen. Particularly, the radially compressive deformation was the only contribution to the linearly volumetric contraction during stress maintenance.
- With the birth of the axial strain, the gel-like constituents around the micro-cavities began to be softened, which created the non-linearly radial strain. Meanwhile, the non-linearly radial strain triggered the development of the non-linearly volumetric deformation of the mortar while using seawater and sand.
- The mortar specimen was scanned for twice besides the original state scan before the peak strength, which was 33.88 MPa. The development of ${\epsilon}_{\mathrm{a}}$ and ${\epsilon}_{\mathrm{v}}$ here accounted for more than half of their peak values, by which the kneaded parental focus gave birth to a baby one. Consequently, the connective region between them was destroyed to be the fragments due to the resultantly global contraction.
- ${\epsilon}_{\mathrm{a}}$ and ${\epsilon}_{\mathrm{v}}$ achieved their peak values at the same stress state, where their values were 1.61 × 10
^{−2}and 1.14 × 10^{−2}, respectively. There lived between the peaks of ${\epsilon}_{\mathrm{a}}$ (or ${\epsilon}_{\mathrm{v}}$) and ${\sigma}_{1}$ the locally high-angle zones of the SSS curves and the local fractures were produced right here. Particularly, the abruptly volumetric dilation was caused by the local fractures that were composed of the interface failure zone of SiO_{2}, the crack zone of the hydrate layers, and the breakage zone of the needle-like AFt. Moreover, the radial tensile strain met a sharp knee corner right in the position where ${\epsilon}_{\mathrm{a}}$ and ${\epsilon}_{\mathrm{v}}$ achieved their peak values. The ${\epsilon}_{\mathrm{r}}$ development dashed out of control afterwards. Coupled with the maximal gradient of the radial tensile strain with the axial load, the partially retrieved elasticity in the axial direction caused the relatively volumetric dilation of the mortar using seawater and sand. - Upon the penetrating cracks’ birth, the neighborhood of the parental foci was thoroughly deteriorated, where the widespread microscopic failure destroyed the reliable support from the local hydrate and the mixture of AFt and feldspar. Consequently, the parental foci with the discontinuousness and the well-blockage effect triggered the Domino damage in the mortar specimen.
- The development of ${\epsilon}_{\mathrm{a}}$, ${\epsilon}_{\mathrm{v}}$, and ${\epsilon}_{\mathrm{r}}$ achieved the coupled effect in the mortar performance, although their behaviors showed the different characteristics. The synchronization of SSS metrization and the damage visualization established in this paper was the crucial approach for research on the physical-chemical-mechanical characteristics of the mortar using seawater and sand and cured in natural seawater.

## Author Contributions

## Funding

## Conflicts of Interest

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**Figure 1.**World fluvial-lacustrine sand resource [3].

**Figure 2.**Quantitative distribution of the key ions and the saline minerals of the seawater specimen (The unit of Q, namely, the quantification, is 10

^{−3}·‰).

**Figure 6.**Micrograph and principal elements’ content from EDS analysis on the composite Portland cement P.C 42.5 R.

Material | Amount (g) |
---|---|

Cement | 1061 |

Sea sand | 803 |

Seawater | 486 (W/C = 0.458) |

Apparent Density (kg/m³) | Packing Density (kg/m³) | Natural Water Content (%) | Methylene Blue Number (‰) | Shell Residuals Contents (%) | Sludge Contents (%) |
---|---|---|---|---|---|

2652 | 1370.3 | 20% | 1.4 | 0.23 | 0.27 |

Results from Normal Sieving Technology | Results from Malvern Mastersizer 2000 Analyzer | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|

d_{10}(μm) | d_{30}(μm) | d_{50}(μm) | d_{60}(μm) | C_{u} | C_{c} | d_{10}(μm) | d_{30}(μm) | d_{50}(μm) | d_{60}(μm) | C_{u} | C_{c} |

1296 | 1615 | 2380 | 3054 | 2.36 | 0.66 | 162.617 | 203.008 | 238.943 | 256.571 | 1.58 | 0.99 |

Initial Setting Time (minute) | Final Setting Time(minute) | Apparent Density (kg/m³) | Compressive Strength for 28 Days (MPa) |
---|---|---|---|

100 | 167 | 3200 | 55.8 |

(a) Tri-Axial Sub-System | ||||||||||||||||||||||||

Outline Dimensions (mm) | Tri-Axial Cabinet | Extreme Loading Conditions | Maximal Stroke of Vertical Main-Shaft (mm) | Accuracies (%) | ||||||||||||||||||||

Diameter(mm) | Height(mm) | Force from Vertical Main-Shaft (kN) | Confining Pressure(MPa) | Deformation Controller | Loading Controller | |||||||||||||||||||

Height: 700 Maximal diameter: 305 Minimal diameter: 225 | 50 | 100 | 500 | 20 | 150 | 0.05 | 0.1 | |||||||||||||||||

(b) MSCT sub-system | ||||||||||||||||||||||||

Gantry mouth diameter(mm) | Coverage width of detector axis Z (mm) | Gantry gradient | Detector material | Detectors sum | Detector channels sum | Detector cooling method | Scanning space accuracy(mm) | Message transmission rate (GB/s) | X-ray generator | |||||||||||||||

Power (kW) | Maximal amperage (mA) | Maximal voltage (kV) | ||||||||||||||||||||||

700 | 24 mm | ±30°± 0.5° | Express rare earth ceramics | 672 | 1344 | Air cooling one | 0.75 | 1.1 | 60 | 500 | 140 | |||||||||||||

(c) MSCT sub-system | ||||||||||||||||||||||||

X-ray generator | Contrast resolution (%) | Spatial resolution(mm) | Image reconstruction matrix dimension | CT value span | Contrast resolution | Spatial resolution(mm) | ||||||||||||||||||

Power(kW) | Maximal amperage (mA) | Maximal voltage(kV) | ||||||||||||||||||||||

60 | 500 | 140 | 0.3 | 0.2 | 1024 × 1024 | [−1024, 3071] | 0.3% | 0.2 |

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## Share and Cite

**MDPI and ACS Style**

WANG, Y.; ZHANG, C.; WANG, J.; XU, Y.; JIN, F.; WANG, Y.; YAN, Q.; LIU, T.; GAN, X.; XIONG, Z. Experimental Study on Foci Development in Mortar Using Seawater and Sand. *Materials* **2019**, *12*, 1799.
https://doi.org/10.3390/ma12111799

**AMA Style**

WANG Y, ZHANG C, WANG J, XU Y, JIN F, WANG Y, YAN Q, LIU T, GAN X, XIONG Z. Experimental Study on Foci Development in Mortar Using Seawater and Sand. *Materials*. 2019; 12(11):1799.
https://doi.org/10.3390/ma12111799

**Chicago/Turabian Style**

WANG, Yajun, Chuhan ZHANG, Jinting WANG, Yanjie XU, Feng JIN, Youbo WANG, Qian YAN, Tao LIU, Xiaoqing GAN, and Zhan XIONG. 2019. "Experimental Study on Foci Development in Mortar Using Seawater and Sand" *Materials* 12, no. 11: 1799.
https://doi.org/10.3390/ma12111799