Method for estimation of compressive strength by in-situ cutting mortar sheet

doi:10.21203/rs.3.rs-3913072/v1

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Method for estimation of compressive strength by in-situ cutting mortar sheet

https://doi.org/10.21203/rs.3.rs-3913072/v1

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To accurately estimate the compressive strength of in-situ cutting mortar sheets, a partially nondestructive testing (PDT) method, namely the innovative shear testing method (STM) is suggested. The mortar sheet from the horizontal masonry joint was removed by drilling a core. Load was applied through the designated STM apparatus to generate approximately pure shear stress and obtain the shear strength of the mortar sheet. The mortar board to withstand pressure from two opposite cone heads was tested and the peak load was recorded when the mortar board fails. The correctness of the test results can be demonstrated by the visible shear failure mode of the mortar sheets. Scattering characteristics were reviewed to check the reliability and repeatability of STM results. The compressive strength measured by STM is closely related to the cube compressive strength, ranging from M2.0 to M16.0. Comparative testing of STM with other available test methods confirmed that STM offers an alternative to in-situ testing of mortar compressive strength. The accuracy of STM is high, and samples extracted from masonry joints can be directly, repetitively, and quickly tested in-situ.

Cutting mortar sheet

masonry mortar strength

compressive strength

in-situ verification

The masonry structure is composed of blocks and can withstand vertical and horizontal loads. The compressive strength of masonry mortar is a crucial parameter for evaluating its reliability, determining structural repairs, conducting accident analysis, and seismic reinforcement. To study the strength of in-situ mortar strength, a simple and non-invasive tests were conducted with non-destructive testing method, and more complex and destructive testing is only carried out at specific locations.

The testing methods for evaluating the compressive strength of in-situ masonry mortar include non-destructive testing (NDT) and partial destructive testing (PDT) methods. However, non-destructive testing such as rebound hammer (Chen et al., 2015), pin penetration test (JGJ/ T136, 2011), DRMS test (Monte et al., 2020 ), and torque penetration test (Marastoni et al., 2017) could cause slight harm to the in-situ mortar. The elastic modulus, penetration resistance, sound velocity and surface hardness are obtained with NDT methods in a low-cost and employing nondestructive means to establish an empirical correlation between the physical test parameter and the compressive strength of concrete. The estimation of the concrete strength based on measured physical quantities is sensitive to local variations in mortar due to differences from laboratory conditions. PDT is more reliable than NDT. Local compression tests (Yang et al., 2016), double impact tests (Łątka and Piotr; 2020), point load tests (Yang et al., 2020) and small sample tests (Drdacky, 2005) have less harmful to the surface of masonry, and damaged masonry surfaces can be repaired.

The studies of Thomas et al., Diakhat é et al., and Malek et al. have indicate that there exists a correlation between the compressive strength and shear strength of certain materials, and shear strength can be converted into concrete cube strength (Reynolds, 2016; Diakhaté et al., 2011; Abd et al., 2016). Mattock and Neil (1972), Iosipescu and A1 (1939), Zhang and Guo (1992), and JSCE-63 (1990) examined the shear strength of raw materials for concrete to establish a functional connection between shear strength and compressive strength of concrete.Cracks forming in the middle of the pure shear section lead to the shear failure of concrete., and the stress field induced by the shear force closely resembles the pure shear stress state, with the shear strength approaching the tensile strength. The shear strength mainly relies on the concrete tensile strength, and the relationship between the shear strength and compressive strength of concrete can be utilized. Yang et al. proposed the Double Shear Test Method (DSTM) using the Double Shear Mechanism to estimate the shear strength of the core, which is related to the compressive strength of concrete. Therefore, the core can be readily tested after being removed from the concrete structure (Yang et al., 2021a). Yang et al. also proposed an innovative in-situ shear test (IST) method for measuring the shear strength of partial concrete cores (Yang et al., 2021b). In accordance with the clamping mechanism principle, the time required for in-situ testing is within 30 minutes.

This study aims to explore the applicability of STM for evaluating mortar strength, which tests mortar sheet collected from brick positions. The testing apparatus was specifically developed for this research. The assessment of test result reliability is conducted considering the failure modes. The strength of STM is related to the compressive strength of mortar cubes, which were cured under the same conditions. STM was also utilized for on-site test verification, it was compared with alternative methods to validate its applicability, reliability, and accuracy.

2.1 Test apparatus

The specially developed STM apparatus is shown in Fig. 2, with a total weight of 7.5 kilograms. The STM apparatus was consists of a counter force frame and load contact component. The counter force frame has sufficient stiffness and would not be deformed during testing. The support force is dispersed through the ring-shaped counter-force frame. The mortar sheets were removed from the horizontal joints for STM testing. Two knifes moving in the same direction generate shear force on the cross-section of the mortar sheet. The lower steel knife is fixed and connected to a pressure sensor, while the upper knife works as a vertical stroke through a rotating handle. The shear load at failure was monitored using a digital recording system capable of accurately recording loads with a precision of 1N.

2.2 Specimen Preparation and Test Procedure

2.2.1 Materials

The strength classification of standard Portland cement is 32.5MPa,which complies with ASTM C150 (2012a). Natural bsilica sand meets the requirements of ASTM C778 (2012b). The sand has a maximum particle size of 2mm, and its average fineness modulus is 2.5. The size of ordinary sintered clay bricks is 240×115×53mm in accordance with ASTM C62 (2012c) and ASTM C652 (2012d). The compressive strength of bricks complies with the requirements of ASTM C67 (2021). Wet the bricks 24 hours before commencing construction, take precautions to prevent the absorption of water by the mortar and ensure thorough hydration of the cement in the mortar.

The mixing proportion of CM is based on the recommended ratios in ASTM C270 (2014) and shown in Table 1. Cement mortar consists of blend of dry portland cement and sand, and mixing manually with a shovel until the mortar has sufficient workability, and check for dry lumps. The compressive strength of these mortar cubes in 50×50×50mm size are tested following ASTM C109/C109M-08 (2012).

Table 1

The mixing proportion of CM.
	Strength grade (MPa)	Cement (Kg/m³)	Medium Sand: (Kg/m³)	Water (Kg/m³)	Lime (Kg/m³)
CM	2.0	170	1487	302	/
	4.0	205	1487	302	/
	6.0	239	1487	302	/
	8.0	264	1487	302	/
	10.0	298	1487	302	/
	12.0	290	1487	302	/
	14.0	310	1487	302	/
	16.0	330	1487	302	/

2.2.2 Samples

Three series of tests, A, B, and C, were conducted. In order to minimize the dispersion of test results, uniform batches of mortar were prepared for all samples. The trained workers prepared all test members within two days. Mortar sheets were extract from 8 masonry columns. The size of the masonry column is 370×490×1500 mm, with a designed mortar strength ranging of M2.0-M16.0. Masonry columns were place outdoors to avoid direct sunlight and rainwater. The material of the mortar cube is fixed as of the corresponding masonry column. All cubic specimens underwent curing in parallel environments to ensure the comparability of test results.Some test photos are shown in Fig. 3.

(1) A-series test

The mortar sheets were tested with STM in 28day curing to check the coefficient of variation caused due to variations in mortar strength and test numbers. After appropriate test numbers were decided, 8 sets of mortar with a strength of M2.0-M16.0 were prepared, and CoVs values were tested at ages of 28d, 60d, 90d, 120d, 150d and 180d.

(2) B-series test

The mortar sheets were removed from the 8 masonry columns. Mortar sheets were subjected to STM at the specific 28d, 60d, 90d, 120d, 150d, 180d, 270d, 300d, 360d. For each testing, three mortar cubes in size of 50×50×50 mm were controlled under compression.

(3) C-series test

Eleven masonry members were drafted and mortar strength tests were conducted at specific 28d, 60d, 90d and 180d using rebound testing, pin penetration testing, STM, point load testing, and LCTM. Series C test does not depend on series A and B tests.

2.2.3 Standard STM testing procedure

Based on series A and B tests, the standard test procedure for evaluating the mortar strength is as follows.

Step 1: Drill the masonry core specimens containing two pieces of bricks and integrated mortar sheet from the horizontal masonry mortar joint of the masonry member (Fig. 4a). Mortar sheet was peel from the sides of the bricks with a chisel. (Fig. 4b).

Step 2: Select intact and undamaged mortar sheets with parallel, smooth, and crack free surfaces. Measure the thickness of the mortar sheet with a vernier caliper, accurate to 0.01 mm (Fig. 4c), and then lay the mortar board flat on the testing surface of the apparatus.

Step 3: Measure the shear load value V with STM apparatus at failure of the mortar sheet (Fig. 4d). When the mortar board does not fail along the shear plane, the test results are considered invalid. The data obtained at the shear failure of mortar sheets is valid, accurate to 1N. Apply he load gradually at a rate of 0.2–0.4 kN/s. The shear strength x of the mortar board is calculated by Eq. (1).

x = V/A (1)

where:

x = shear strength of mortar sheet, in MPa;

V = shear load at the mortar sheet damaged, in N;

A = shear area of the mortar sheet, in mm².

3.1 Select test numbers

Determine the dispersion of STM test data and the impact of test frequency on STM results through A-series testing using coefficient of variation (CoV). From Fig. 5,it is observable that as the mortar strength increases, CoV slightly decreases. When the number of tests increases by 6, the COV of each mortar strength will increase. When the number of tests exceeds 4, the CoV is basically less than 10%. To simplify testing, the mean value of the four test results is determined as the standard test result. Figure 9 shows the COV range of STM test results from 8–14%. The 28 day CoV values for mortar cube test, double impact test, spiral pull-out test, and penetration test were 11%, 25%, 20%, and 12%, respectively (Pelà et al., 2018). The dispersion of STM test results is higher than other methods and close to the cube test results.

3.2 Stability of Test Results

The COVs of the STM test values of CM mixtures at 28, 60, 90, 120, and 180 days are given in Fig. 6. Each COV at different testing ages was taken from six samples. The CoV curve fluctuates with the increase of age, with each intensity corresponding to a CoV of 5%-12%, indicating that the age has less effect on the strength of the measured mortar sheet. The cov of 6 STM test values is almost less than 10%, and the accuracy of the test results is acceptable.

3.3 Empirical relationship between STM and cube compressive strength of mortar

Series B testing was conducted to establish the correlation between cube strength and STM strength. The standard test methods summarized above was followed for STM test. Figure 7 illustrates the correlation between STM and mortar compressive strength. The regression form y = ax^b is adopted as the best-fit line to represent the relationship. Symbol x represents the STM strength of the mortar, which is calculated by Eq. (1). Symbol y is the compressive strength of masonry cube, in MPa. Figure 7 indicates a strong correlation between STM and mortar cube strengths determined using the power function format, irrespective of the age and strength of the morta. The correlation coefficient (R²) of the power function equation is 0.96.

3.4 Verification and Accuracy of the STM

Verify the accuracy, applicability, and reliability of the equations obtained from STM tests by comparing different methods of C-series experiments. The compressive strength of masonry mortar was assessed using the rebound method, penetration method, LCTM, point load test, crushing test and STM (Fig. 8).

Table 2 summarizes the NDT and PDT test results obtained for different age groups. The maximum error in testing the rebound method yields a mortar compressive strength of 38.22%, and the maximum error in testing the compressive strength of mortar by the penetration method is 32.55%. Higher penetration values can be measured using harder mortars. The rebound test value after 60 days can reflect the changing trend of the compressive strength of the mortar. The limitation of non-destructive testing technology is that it can only evaluate the surface properties of mortar joints, which has a greater impact on the rebound method and penetration method. The accuracy of pin penetration test results is much higher than that of the rebound method.

The maximum errors for the crush test, PLT, and LCTM were 19.24%, 14.65%, and 15.83%, respectively. The strength of the PDT test at typically greater than the actual uniaxial compressive strength of the mortar. The mortar strengths evaluated by the point loading method, STM and crushing test methods are all significantly higher, especially when the mortar strength is higher. The mortar evaluated by the crushing method has the highest compressive strength. For PDT, the limitations of NDT can be addressed by extracting masonry sheet from deep joints. When squeezed, the mortar inside the masonry is denser than the mortar at the edges. Excess moisture in the mortar inside the masonry is easily absorbed by the bricks, while moisture in the edge mortar is less easily absorbed or is more severely affected by the environment. The strength of the edge mortar is therefore rather low.

The C series of experiments verified that the precision of the PDT method surpasses that of the NDT method. There is a strong correlation between STM strength and mortar cube strength. The maximum error of STM is less than 10%, and STM testing can obtain the most accurate results compared with other methods. STM can eliminate the limitations of DPT and achieve more accurate results.

Table 2

Comparison of compressive strength of mortar using four differen methods.
		Rebound test (GB/T50315, 2011)		Penetration test (JGJ/T 136, 2011)		STM		Crush test (Yang et al., 2022)		Point-load test (Yang et al., 2020)		LCTM (Yang et al., 2016)		Compressive strength of mortar (MPa)
		Estimated strength (MPa)	RD (%)	Estimated strength (MPa)	RD (%)	Tested strength (MPa)	RD (%)	Estimated Strength (MPa)	RD (%)	Tested strength (MPa)	RD (%)	Estimated strength (MPa)	RD (%)	Compressive strength of mortar (MPa)
28d	M10.0 CM masonry	10.10	-15.11	11.21	-5.81	11.19	-5.98	10.76	-9.58	10.73	-9.87	10.89	-8.45	11.9
	M8.0 CM masonry	6.70	-19.25	5.59	-32.55	7.35	-11.47	7.78	-6.24	7.45	-10.25	7.051	-15.04	8.3
	M6.0 CM masonry	4.47	-31.24	5.17	-20.39	5.79	-10.97	6.05	-6.87	5.66	-12.89	7.1	10.24	6.5
60d	M2.0 CM masonry	1.98	-38.22	2.33	-27.06	2.93	-8.57	2.94	-8.26	2.73	-14.65	3.03	-5.29	3.2
	M6.0 CM masonry	4.82	-32.07	5.79	-18.41	6.61	-6.89	8.47	19.24	6.76	-4.73	6.5	-7.62	7.1
	M10.0 CM masonry	11.11	-17.12	13.91	3.80	12.52	-6.58	12.11	-9.65	14.43	7.66	11.33	-15.43	13.4
90d	M6.0 CM masonry	7.89	-10.25	7.28	-17.32	8.32	-5.47	9.69	10.21	9.47	7.61	7.41	-15.83	8.8
90d	M2.0 CM masonry	2.92	-21.16	3.62	-2.03	3.41	-7.87	3.53	-4.72	3.38	-8.52	3.37	-8.98	3.7
180d	M16.0 CM masonry	20.54	9.23	20.03	6.53	17.5	-6.89	20.72	10.21	20.05	6.63	20.65	9.83	18.8
	M8.0 CM	9.57	-8.81	11.49	9.48	9.62	-8.36	11.84	12.76	10.75	2.35	11.10	5.76	10.5
	M10.0 CM masonry	10.10	9.05	11.21	4.32	12.99	-5.87	10.76	13.83	10.73	6.38	10.89	8.56	13.8
Mean of absolute value of RD			18.95		13.35		7.51		10.43		8.28		10.72
Note: Relative deviation RD = 100×(Estimate of the compressive strength of mortar cube) / the actual compressive strength of mortar cube.

In situ testing has verified the applicability, reliability, and accuracy of STM test in actual projects. STM is implemented in a brick building in Xinba Town, Jiangsu Province, China (see Fig. 9). The building is constructed with 240×115×53 mm clay bricks and cement mortar.

STM tests were performed on four different walls on each floor of the building to assess the spatial variability of the material properties utilized. Mortar cubes are composed of the same mortar materials as masonry buildings during construction and are situated in identical surroundings as masonry structures for curing. Three mortar cube samples were tested at each selected location in the laboratory and the strength of the tested mortar cubes was compared with the estimated STM values. The test values obtained using STM are converted into mortar cube strengths via the curve described in section 3.3. The results obtained at different locations of masonry buildings are shown in Table 3. The CoVs for STM at each test location range from 5.13 to 12.48%. The in-situ test results of STM can be deemed to be on the safe side. The effectiveness of the STM proposed in this paper for in-situ mortar strength testing is confirmed. In-situ verification shows that the compressive strength of the cube estimated by STM is about 1.82–14.09% lower than the measured strength of the mortar cube. It can be considered that the quality of in-situ mortar is always worse than that of the laboratory, which may lead to a significant decrease in estimated strength.

Table 3

In-situ verification for existing masonry buildings with STM
Story	Parameter	Wall 1 (MPa)	Wall 2 (MPa)	Wall 3 (MPa)	Cube strength
First-story	STM estimated strength	10.41	10.45	8.92	11.0
		10.95	10.67	9.79
		9.83	9.94	10.27
		9.64	11.25	9.32
	Average	10.18	10.53	9.45
	Relative deviation (%)	-7.45	-4.27	-14.09
	Standard deviation	0.59	0.54	0.64
	CoV (%)	5.79	5.13	6.77
Second-story	STM estimated strength	9.8	10.3	8.7	11.7
		9.7	11.3	10.5
		9.1	10.8	11
		11	12.4	11.8
	Average	9.9	11.2	10.5
	Relative deviation (%)	-10.01	-1.82	-4.55
	Standard deviation	0.79	0.89	1.31
	CoV (%)	7.98	7.95	12.48

(1) STM proposed in this article can be utilized to indirectly predict the compressive strength of mortar. Unlike other shear testing methods, STM can generate pure shearing stress within the specimen. The test shear strength is closer to the actual tensile strength, so the STM strength is more related to the compressive strength. The apparatus used are portable and convenient for on-site use.

(2) The strength of STM and cube was tested and a direct and reliable correlation between them was obtained. At least four samples should be used to meet the minimum sample size requirement.

(3) The results of STM are intuitive, and the anomalous failure mode of the sample can be disregarded as invalid data. The formula correlation coefficient (R²) between shear strength and mortar compressive strength in the form of a power regression equation is 0.96. The strength under compression exhibited by mortar cubes has a good correlation with the STM test results, with mortar strength ranging from M2.0 to M16.0.

(4) The comparison with other testing methods has verified that the test results of STM are accurate, with an error of less than 10%. STM can reliably estimate the compressive strength of the mortar employed in masonry constructions. Further research is recommended to verify the application of STM in other mortar types with different curing ages.

Author Contribution

Suhang Yang: Data analysis and Writing.Xiaoyun Cao: Formal analysis.Zhifeng Xu: Validation; Methodology.

ACKNOWLEDGMENTS

This study is supported by the Opening Foundation of Shandong Key Laboratory of Civil Engineering Disaster Prevention and Mitigation (Grant No. CDPM2019KF10), the National Natural Science Foundation of China (Grant No. 51908341) and the National Key R & D Program of China (Grant No. 2018YFD1100402-05), Opening Foundation of Key Laboratory of concrete and prestressed concrete structure, Ministry of education, Southeast University (Grant No. CPCSME2019-06).

DATA AVAILABILITY STATEMENT

Some or all data, models, or codes that support the findings of this study are available from the corresponding author upon reasonable request.

Abd Malek, Nor Jihan, et al. (2016) Double shear test behaviour of balau species for different end distance. Jurnal Teknologi 78(5-4): 89-93.DOI:10.11113/jt.v78.8556.
ASTM C150 (2012a) West Conshohocken, PA: ASTM. ASTM. Standard specification for standard sand.
ASTM C778 (2012b) West Conshohocken, PA: ASTM. ASTM. Standard test method for compressive strength of hydraulic cement mortars (using 2-in. or [50-mm] cube specimens).
ASTM C62 (2012c) West Conshohocken, PA: ASTM. ASTM. Specification for hollow brick (hollow masonry units made from clay or shale).
ASTM C652 (2012d) West Conshohocken, PA: ASTM. ASTM. Specification for Portland cement.
ASTM C270-14a (2018) West Conshohocken, PA: ASTM. ASTM. Standard test method for water retention of hydraulic cementbased mortars and plasters.
ASTM C109/ C109M (2012) West Conshohocken, PA: ASTM. ASTM. . Standard test methods for in situ measurement of masonry mortar joint shear strength index.
ASTM C67/C67M (2021) Standard Test Methods for Sampling and Testing Brick and Structural Clay Tile.
ASTM C270 (2019) Standard Specification for Mortar for Unit Masonry
Chen, D. C., T. Z. Chen, and C. X. Shi (2012) Research on the evaluation of strength for fired common brick in existing masonry structures in rebound method. J Hunan Univ 39 (3): 23-27.
Chinese Standards (2011) Technical standard for site testing of masonry engineering. GB/T50315. Beijing: National Standard of the People’s Republic of China.
Chinese Standards (2011) Technical specification for testing compressive strength of masonry mortar by penetration resistance method. JGJ/T 136. Beijing: National Standard of the People’s Republic of China.
Del Monte, Emanuele, Sonia Boschi, and Andrea Vignoli (2020) Prediction of compression strength of ancient mortars through in situ drilling resistance technique. Construction and Building Materials (237): 117563.DOI:10.1016/j.conbuildmat.2019.117563.
Diakhaté, Malick, et al. (2011) Experimental investigation of tack coat fatigue performance: Towards an improved lifetime assessment of pavement structure interfaces. Construction and Building Materials 25(2): 1123-1133.DOI:10.1016/j.conbuildmat.2010.06.064.
Drdacky, M. (2005) Identification of historic materials using tests on small samples. 2nd international conference on hazards and modern heritage, Kos, Greece.
Felicetti, Roberto, and Natalino Gattesco (1998) A penetration test to study the mechanical response of mortar in ancient masonry buildings. Materials and Structures (31): 350-356.DOI:10.1007/bf02480678.
Iosipescu, N., and A1 Negoita (1969) A new method for determining the pure shearing strength of concrete. Concrete (London) .
JSCE, SF (1990) Method of test for shear strength of steel fiber reinforced concrete (SFRC). Japan Society of Civil Engineers, Tokyo.
Łątka, Dawid, and Piotr Matysek (2020) Determination of mortar strength in historical brick masonry using the penetrometer test and double punch test. Materials 13(12): 2873.DOI:10.3390/ma13122873.
Marastoni, Diego, et al. (2017) Torque Penetrometric Test for the in-situ characterisation of historical mortars: fracture mechanics interpretation and experimental validation. Construction and Building Materials (157): 509-520.DOI:10.1016/j.conbuildmat.2017.09.120.
Mattock, Alan H., and Neil M. Hawkins (1972) Shear transfer in reinforced concrete—Recent research. Pci Journal 17(2): 55-75.DOI:10.15554/pcij.03011972.55.75.
Pelà, Luca, Pere Roca, and Alessandra Aprile (2018) Combined in-situ and laboratory minor destructive testing of historical mortars. International Journal of Architectural Heritage 12(3): 334-349.DOI：10.1080/15583058.2017.1323247
Reynolds, Thomas, et al. (2016) Dowelled structural connections in laminated bamboo and timber. Composites Part B: Engineering (90): 232-240.
Yang, Suhang, Ruinan Gu, and Shuangyin Cao (2016) New local compression test to estimate in situ compressive strength of masonry mortar. Journal of Testing and Evaluation 44(1): 67-76.DOI：10.1520/JTE20130088
Yang, Suhang, et al. (2020) Point-load test method for estimation of in situ masonry mortar strength. Journal of Materials in Civil Engineering 32(10): 04020286.DOI:10.1061/(ASCE)MT.1943-5533.0003347.
Yang, Suhang, Haidong Zhu, and Zhifeng Xu (2021) Prediction of compressive strength of concrete using double-shear testing method. Journal of Materials in Civil Engineering 33(1): 04020423.DOI:10.1061/(ASCE)MT.1943-5533.0003505.
Yang, Suhang, Zhifeng Xu, and Zhengning Bian (2021) COMPRESSIVE STRENGTH OF CONCRETE USING INNOVATIVE IN-SITU SHEAR TESTING METHOD. Revista Romana de Materiale 51(2): 281-290.
Yang, Suhang, Chaoran Duan, and Zhifeng Xu (2023) Crush test method for determining compressive strength of mortar. Materials and Structures 56(1):DOI: 21.10.1617/s11527-023-02113-z
Zhang, Qi, and Z. H. Guo (1992) Study on shear strength and shear deformation of concrete. Journal of Building Structures 13(5): 17-24.

No competing interests reported.

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You are reading this latest preprint version

Method for estimation of compressive strength by in-situ cutting mortar sheet

Status:

Version 1

Abstract

Figures

1. Introduction

2. Test work

2.2 Specimen Preparation and Test Procedure

2.2.1 Materials

2.2.2 Samples

2.2.3 Standard STM testing procedure

3. Test results and discussion

3.1 Select test numbers

3.2 Stability of Test Results

3.3 Empirical relationship between STM and cube compressive strength of mortar

3.4 Verification and Accuracy of the STM

4. In-situ verification of STM

Conclusions

Declarations

Author Contribution

ACKNOWLEDGMENTS

DATA AVAILABILITY STATEMENT

References

Additional Declarations

Status:

Version 1