1. Purbanchal University, HIST Engineering College, Nepal; bikashrestha61@gmail.com
2. Purbanchal University, HIST Engineering College, Nepal; bparajuli@outlook.com
3. Joint Secretary, Government of Nepal, Nepal; jrjyoti@yahoo.com
4. Nepal Bureau of Standards & Metrology, Nepal; thapamagaraarati@gmail.com

*             Correspondence: bikashrestha61@gmail.com

Keywords: hydraulic cement, curing temperature, compressive strength

1. INTRODUCTION

Portland cement underpins the global construction industry as a concrete binder. The cement matrix and curing conditions affect concrete’s compressive strength and other mechanical properties. In concrete structures, the load-bearing capacity and longevity are determined by the compressive strength of the concrete.  There is a significant relationship between the curing temperature and the compressive strength of concrete. In order to facilitate the reaction of cementitious materials into a robust matrix, proper curing necessitates the presence of sufficient moisture and temperature during the initial hydration phase. Different temperatures are used for curing at different construction sites in the real world. Changes in the seasons, geographical location, and the logistics of construction can all have an impact on the strength and resilience of concrete structures. There is a need for additional targeted research on curing temperature and hydraulic cement, despite the fact that there has been a significant amount of research conducted on the effect of curing temperature on compressive strength. In order to optimise concrete construction techniques, improve structural quality and longevity, and address issues related to construction sustainability, it is essential to have a nuanced understanding of this relationship. Through the methodical investigation of variations in curing temperature and the effects those variations have on the compressive strength of hydraulic cement, the purpose of this research is to fill the knowledge gap. In order to determine the relationship between curing temperature and compressive strength, this study employs controlled experiments, statistical analyses, and data analysis. This study has the potential to advance cement behaviour science as well as the construction manufacturing sector. The results of this study will contribute to the development of construction methods that are more resilient, sustainable, and efficient. One of the most widely used hydraulic cementitious materials in the construction industry is Portland cement. The most common type of cement that is used in the production of concrete, mortar, and other building materials is this type. At the beginning of the 19th century, Joseph Aspdin in England developed it by combining it with other types of hydraulic lime. Limestone is typically used in its production. The process involves heating limestone and clay minerals in a kiln, grinding the clinker, and adding between 2 and 3 percent gypsum. The end product is a fine powder. Portland cement is available in a wide variety of forms. While the majority of Portland cement is grey, there is also white cement available. Because of its resemblance to Portland stone, which is native to the Isle of Portland in Dorset, it was given that name. In the year 1824, Joseph Aspdin assigned it a name and patented it. In the 1840s, his son William Aspdin invented “modern” portland cement (Courland, Robert, 2011). Portland cement is a cheap building material because limestone, shales, and other natural materials are cheap and abundant. It is mostly used to make concrete, a mixture of aggregate (gravel and sand), cement, and water. The construction industry shapes society’s infrastructure, and concrete structures’ durability and strength are crucial for their long-term functionality and safety. Concrete, which is a mixture of aggregates, water, and cement, is the material that is used in modern construction. The compressive strength of concrete has an impact on the structural integrity and load-bearing capacity of structures such as roads, bridges, dams, and buildings respectively.  Concrete’s compressive strength is significantly impacted by the curing process. In order to facilitate hydration reactions, cementitious materials must be cured, which requires an adequate amount of moisture, temperature, and adequate time. In order to achieve the desired mechanical properties of concrete, proper curing is necessary because it creates sufficient bonding and crystalline structure. It is possible for strength, durability, and structural failure to be reduced by improper curing. Temperature during the curing process has an effect on the rate of cementitious matrix hydration reactions as well as the extent of those reactions. The connection between the temperature at which the material is cured and its compressive strength is complicated by the presence of chemical reactions, microstructural changes, and hydration products. Despite the significance of the topic, additional research is required to investigate the effects of curing temperature on the compressive strength of hydraulic cement. Compressive strength of a material refers to its resistance to axial loads or forces that put it under pressure or cause it to be compressed. It is crucial for evaluating concrete, rocks, and soils’ performance and durability (Beer, Jr., & DeWolf, 2014).  Compressive strength is a key mechanical property of concrete that affects structure suitability, durability, and safety. Compressive strength is a key structural performance parameter for concrete (Mindess S. Y., 2003). Concrete’s resistance to axial loads or compression is ascertained through this method. Cement, an essential component of concrete, has a significant impact on the material’s compressive strength. To design and construct concrete structures that are long-lasting, it is essential to have a solid understanding of the compressive strength of cement.  The ability of a concrete structure to withstand loads without deforming or failing is determined by its compressive strength. In order to construct a building, bridge, pavement, dam, or any other type of critical infrastructure, compressive strength is absolutely necessary. The concrete that makes up a structure needs to be able to withstand the stresses and strains that are caused by loads. Compressive strength that is insufficient can result in deformation, cracking, and collapse, putting the occupants and users of the structure in danger. The compressive strength of concrete has an impact on the engineering and design of structures with concrete. Engineers design members and choose reinforcement based on compressive strength to meet safety and design standards. A higher compressive strength allows slimmer members to carry the same load, making design more efficient.

2. LITERATURE REVIEW

Concrete structures are expected to last long and withstand freeze-thaw cycles, chemical exposure, and moisture ingress. Concrete durability depends on compressive strength. The concrete matrix density and impermeability are both increased by the compressive strength, which in turn reduces the amount of moisture and harmful substances that are able to enter the structure. Because of this, the structure will last longer. When it comes to construction, pouring, placing, and compacting fresh concrete to the desired shape and dimensions are all necessary steps. The ability of concrete to be handled and placed without cracking or deforming is facilitated by its compressive strength. A sufficient compressive strength enables the removal of formwork at the appropriate time and reduces the amount of early-age damage that occurs during construction. In order to ensure that the design specifications are met, it is necessary to monitor and control the compressive strength of the concrete both during and after construction. For the purpose of ensuring that the design strength is met, quality control testing involves compressing concrete samples. The structure will function as intended thanks to this process, which also helps to reduce the number of unexpected failures. There is a correlation between the compressive strength of cement and the performance, safety, and durability of concrete structures. From the planning and building stages to the actual operation, it is essential. Having an understanding of compressive strength and being able to effectively manage it enables engineers and construction professionals to construct long-lasting concrete structures that improve both safety and sustainability. On account of its topography and geography, Nepal is home to a wide range of climates. This causes regional temperature differences. Regional temperature variations in Nepal based on climate zones: In southern Nepal, the Terai has a subtropical climate. Higher temperatures than other parts of the country are typical. In summer (May–September), temperatures can reach 35°C (95°F). The region is warmer year-round due to mild winter temperatures of 10°C to 25°C (50°F to 77°F). The Nepalese hills are temperate. There are seasons and moderate temperatures. From March to June, summer temperatures are 15°C to 25°C (59°F to 77°F). Winter temperatures can drop to 0°C to 15°C (32°F to 59°F), especially in higher elevations. Due to higher elevations, the Himalayas have a cold, alpine climate. Season and altitude greatly affect temperatures. Winter temperatures in high mountains can drop to -20°C (-4°F) or lower. These areas have cool summers, 0°C to 15°C (32°F to 59°F). Kathmandu, in central Nepal, has a temperate climate with seasons. April to June summer temperatures are 20°C to 30°C (68°F to 86°F). December to February are cooler, with temperatures around 10°C.  The lower elevation of Pokhara, a popular tourist destination, makes it milder than the high mountains. From April to June, summer temperatures are 20°C to 30°C (68°F to 86°F). December to February have mild winters with daytime temperatures around 15°C (59°F). Concrete strength depends on cement hydration, a complex chemical process. Cement particles react with water to form hydration products. Water reacts with cement compounds like tricalcium silicate (C3S) and dicalcium silicate (C2S) to form calcium silicate hydrate (C-S-H) gel and calcium hydroxide (CH). Dissolving cement particles in water starts cement hydration, followed by nucleation and growth. The C-S-H gel binds, while CH crystals build long-term strength (Scrivener, K. L., Juilland, P., Monteiro, P. J., & Mohamed, A. A., 2015). Over time, the C-S-H gel grows and densifies, filling voids and pores in the mixture and improving concrete’s mechanical properties (Mindess  & Concrete, 2015). Concrete strength depends on hydration, which is affected by water-cement ratio, curing conditions, and temperature. Higher hydration increases concrete strength. The C-S-H gel forms a network of interlocking particles that strengthens the concrete matrix (Scrivener, Advances in understanding hydration of Portland cement, 2015). In conclusion, cement hydration is essential to concrete strength. Hydration products, especially C-S-H gel and CH crystals, bind and densify the concrete matrix, increasing mechanical strength over time. Concrete structure strength depends on weather. Temperature, humidity, and weather can affect concrete hydration and mechanical properties (Neville, Properties of Concrete, 2011). Temperature changes affect cement hydration. Higher temperatures accelerate hydration reactions, accelerating early strength gain. Extreme heat can cause thermal cracking and excessive water evaporation, compromising concrete’s durability (Neville, Properties of Concrete, 2011). Alternatively, cold weather can slow hydration and strength development. Ice in concrete pores during freezing temperatures can cause internal pressure, microcracks, and reduced strength (Neville, Properties of Concrete, 2011). Another important factor is humidity. Rapid evaporation of water from freshly placed concrete can cause surface shrinkage cracks, compromising structure integrity in dry climates. Such conditions require proper curing methods like covering the concrete with wet burlap or using curing compounds to maintain moisture levels and strength development (Neville, Properties of Concrete, 2011). Early curing exposure to rain and moisture can also reduce strength. Rainwater can remove cement particles and disrupt hydration, reducing strength and durability (Neville, Properties of Concrete, 2011). Construction practices must consider mix designs, curing methods, and protective measures to reduce weather effects on concrete strength development. Climate adaptation can help concrete achieve the desired strength and durability over its service life (Neville, Properties of Concrete, 2011). Several studies have examined how curing temperature affects hydraulic cement-based concrete compressive strength. These studies have illuminated the relationship between curing conditions and concrete performance. Lee and Kim (2015) examined how curing temperature affects cementitious material hydration. The researchers found that elevated curing temperatures accelerated early-stage hydration reactions, increasing early-age compressive strength using isothermal calorimetry and thermogravimetric analysis. However, the study stressed the importance of balancing early strength gain and long-term durability (Lee, 2015). Concrete compressive strength was examined by Smith et al. (2017) at different curing temperatures. The researchers tested ambient and elevated curing temperatures. They found that higher curing temperatures increased initial strength but decreased it over time (Smith, J., Johnson, R., & Brown, A., 2017). Chen and Li (2018) examined how curing temperature affects concrete microstructure at different ages. They found that higher curing temperatures accelerated calcium silicate hydrate (C-S-H) gel formation, improving compressive strength using advanced imaging. The literature provides valuable insights into how curing temperature variations affect hydraulic cement-based concrete compressive strength, but several research gaps and unexplored aspects warrant further investigation.  Concrete structures often face environmental conditions beyond ideal temperature. Most research examines variation by high curing temperature, but concrete structures are also exposed to cold or freezing weather. Understanding how higher and lower curing temperatures interact could improve concrete performance predictions in real life. Most research focuses on ordinary portland cement-based concrete. Other hydraulic cement types, such as Pozzolana cements, have yet to be studied for curing temperature effects. The behaviour of these cement under different curing temperatures could reveal their performance under different environmental exposure conditions and expand the research. Many studies offer insights based on specific experimental conditions, but a statistical analysis of data across curing temperatures and concrete mixes is lacking. A systematic analysis of result variability and reliability could strengthen research conclusions. The effects of curing temperature variations have been studied, but practical guidelines, quality control methods, and national and international standards for construction industry professionals have yet to be developed. Engineers and contractors can improve concrete performance with practical curing strategies for different weather conditions.

3. MATERIALS AND METHODS

An experimental research design has been adopted to investigate the effects of curing temperature variations on the compressive strength of hydraulic cement as mentioned in figure 01.

Figure 01: Framework of Research Methodology

Cement samples are collected from industry’s silo and from market randomly. Mortar cubes are casted with the cube of size 70mm*70mm*70mm in controlled laboratory environment. These samples are undergone for different curing temperature regimes, including standard curing temperature (27±2)°C as reference temperature to calculate the variation, elevated temperatures upto 40°C representing hottest weather of concrete exposure, and low-temperature upto 5°C representing coldest weather conditions. Compressive strength tests are performed using the calibrated compression testing machine after specified curing durations. The data collected have been analyzed statistically to identify trends and correlations between curing temperature variations and compressive strength outcomes. Data collection is a crucial phase of this research process, allowing for the empirical analysis of the relationship between curing temperature variations and the resulting compressive strength of hydraulic cement. The compressive strength test of mortar cube is conducted by using the calibrated compression testing machine after the specified curing durations. The axial loads are applied to specimen until failure occurred, and the maximum load sustained is recorded. This load is used to calculate the compressive strength of each sample. The replicate test of multiple samples is conducted to ensure the reliability of results for each curing temperature regime. This approach enables the calculation of average compressive strength and ensures statistical significance. The compressive strength data for each sample, along with corresponding curing conditions, are meticulously recorded. A well-organized data storage system is established to prevent data loss and facilitate subsequent analysis. The cement samples were selected in such a way that production capacity of brand and their market coverage in Nepalese market and easy availability in market. The representative cement manufactured by Huaxin Cement Pvt. Ltd. in Dhading from random market in Kathmandu was collected as a test sample which is the second largest cement industry in Nepal with production capacity 3000 ton per day.  Another samples of AMBE cement, Sarbottam cement and Trishakti (Narayani) were collected from factory’s silo for laboratory test. These samples were tested by cuing at 5° C to 40° C. The cement test specimens were prepared in 1:3 ratio i.e. one part of cement and three parts of standard sand. The standard sand used in mortar mix having three different grades as prescribed by Indian Standard (IS 650:1991). The water used in mortar mix was treated and free from organic matters and other impurities. The sampled cements and sand used are shown in Figure 2, 3 and 4.

Figure 02: Sample from Market, Figure 03: Sample from Silo, Figure 04: Standard Sand of Three Grades

The laboratory test for determination of compressive strength of cement was conducted as per procedure prescribed by NS 123:2041. This method of test covers the procedure for determining the cubes compacted by means of a standard vibration machine.  For the variation analysis, compressive strength of cement at the standard temperature of (27± 2)°C was taken as reference.

3.1 Vibrating Machine

The vibrating machine used in this test consists of a frame mounted on coil spring to carry the cube mould, and a revolving shaft provided with an eccentric. By means of a balance weight beneath the base plate attached rigidly to the frame, the centre of gravity of the whole machine, including the cube and mould, was brought either to the centre of the eccentric shaft, or within a distance of 25mm below it. The machine was constructed to comply with the following essential requirements:

Table 01: Requirements of Vibrating Machine (NS 123:2041, NBSM, 2041)

Descriptions	Specifications
Weight of Machine on its supporting Springs (excluding weight of solid eccentric, but including weight of mould, mould clamp, hopper and cement cube)	30±1 kg
Out of balance moment of eccentric shaft	0.00161297 kg
Normal running speed of eccentric shaft	12000±400 rpm

3.2 Preparation of Test Specimens

The test specimens were in the form of cubes having area of face equal to 50 cm2. The height of the moulds and the distance between the opposite faces were 70.60 mm. Each mould was provided with a base plate having a plane surface machined to a tolerance 0.15 mm and made of non-absorbent material.

3.3 Mix Proportions and Mixing

The mixing and proportioning of cement and sand was performed at the laboratory temperature of (27± 2)°C. The dry cement sand mix of 1:3 by weight was prepared by using trowel and specified quantity of water was added to prepare cement sand mortar. The material for each cube was mixed separately and the quantity of cement, standard sand and water was as follows:

Cement:  200 g

Standard sand: 600 g

Water: Percent of combined weight of cement and sand, where P is the percentage of water required to produce a paste of standard consistency.

3.4 Moulding Specimens

The mould assembly was placed on the table of vibrating machine and the prepared mix was placed in the cube mould immediately after mixing. The mortar was prodded 20 times to ensure elimination of entrained air and honey combing and vibrated at the speed of 12000±400 vibrations per minutes. At the end of vibration, the mould was removed with base plate from the machine and top surface of the cube was finished by smoothing the surface with the blade of a trowel.

3.5 Curing Specimens

The filled moulds were kept at a temperature of (27± 2)°C in atmosphere of at least 90 percent relative humidity for 24 hours after completion of vibration. At the end of that period mould was removed and mortar cube was submerged in clean fresh water for specified period at pre set temperature.

3.6 Testing

Three cubes were tested for compressive strength at a period and the compressive strength was the average of the strengths of the three cubes for each period of curing. The cubes were tested on their sides without any packing between the cube and the steel platens of the testing machine. One of the platens was carried on a base and it was self-adjusted, and the load was uniformly applied, starting from zero at a rate of 350 kg/cm²/min. The analysis of variation in compressive strength of hydraulic cement due to curing temperature variations involves a comprehensive examination of the relationship between the curing temperature and the resulting compressive strength of the cement samples. This type of research is critical for understanding how temperature fluctuations during the curing process can impact the ultimate strength and performance of cement. The data and results analysis plays a pivotal role in drawing meaningful conclusions from the experimental study

4. RESULTS

These samples were used for analysis of variation in cement compressive strength due to low curing temperature variation in this phase. Regression analysis is a powerful statistical technique used to analyze the variation in the compressive strength of hydraulic cement due to curing temperature variations. It helps researchers and engineers understand the relationship between these variables and it helps to quantify the variations in compressive strength that enable the engineers and designers to accommodate this variation in design. All the laboratory test of this research is performed according to NS 123:2041 [Method of Physical Test for Hydraulic Cement] which recommend the curing temperature of mortar cube for compressive strength testing is (27±2) °C as far as possible. This curing temperature recommended by NS 123:2041 is higher than the temperature of curing water recommended by other international standards. The experimental data of this research shows that the compressive strength of hydraulic cement decreases with decreasing curing temperature and increases with increasing curing temperature of water. Developing countries are the major cement consumers of the world so the quality of cement and cement products directly impacts the reliability of physical infrastructure and economic growth of the countries. There are various international standards to standardize the cement quality, its requirements and test methods. In the context of Nepal, cement industries are mandatorily required to produce various grades of cement which comply with NS 49 for OPC cement, NS 385 for PPC cement, NS 384 for PSC cement and NS 572 for OPC 43 and 53-grade cement. Nepal Bureau of Standards and Metrology provides Nepal Standard certification to   OPC, PPC, PSC, OPC 43 grades and OPC 53 grades. This is the regulatory body for the standards implementation and quality monitoring of cement. NBSM  developed the NS 123 for the testing of physical requirements of the hydraulic cement that specify the temperature of curing water as (27±2) °C which is higher than the curing temperature recommended by ISO 679:2009, BS EN 196 – 1: 2016 and ASTM C109/C109M. The experimental data of this research shows that the curing temperature recommended by NS 123 is more liberal in terms of quality assessment and monitoring than other international standards. The compressive strength of hydraulic cement samples used for laboratory tests at the curing temperature recommended by various international standards is determined by using the regression equation formulated in the previous section.

OPC 43 Grade Cement Sample

As per BS EN 196 – 1: 2016, (20±1) °C

3 days, compressive strength = 40 Mpa

7 days, compressive strength = 44 Mpa

28 days, Compressive strength = 50 Mpa

As per ISO 679: 2009, (20±1) °C

3 days, compressive strength = 40 Mpa

7 days, compressive strength = 44 Mpa

28 days, Compressive strength = 50 Mpa

As per ASTM C109/109M, (23±2) °C

3 days, compressive strength

From equation (1),

                                                                    = 28.8879609 + 0.55358302 * 23

                                                                    = 41.62 ≈ 42 Mpa

7 days, compressive strength

From equation (2),

   = 34.1285809 + 0.63362047 * 23

                                                                   = 48.70 ≈ 49 Mpa

28 days, compressive strength

From equation (3),

                                                                    = 37.178456 + 0.6772004 * 23

                                                                    = 52.75 ≈ 53 Mpa

PPC Cement Sample

As per BS EN 196 – 1: 2016, (20±1) °C

3 days, compressive strength = 20 Mpa

7 days, compressive strength = 28 Mpa

28 days, Compressive strength = 37 Mpa

As per ISO 679: 2009, (20±1) °C

3 days, compressive strength = 20 Mpa

7 days, compressive strength = 28 Mpa

28 days, Compressive strength = 37 Mpa

As per ASTM C109/109M, (23±2) °C

3 days, compressive strength

From equation (4),

                                                          = 12.39750312 + 0.390736579 * 23

                                                                    = 21.38 ≈ 21 Mpa

7 days, compressive strength

From equation (5),

   = 14.9146536 + 0.66351748 * 23

                                                                   = 30.17 ≈ 30 Mpa

28 days, compressive strength

From equation (6),

                                                                    = 19.9237297 + 0.84660112 * 23

                                                                    = 39.39 ≈ 39 Mpa

Table 02: Comparative Results of Sample Tested

S.N.	Test Method	Cement Type	Testing Period	Compressive Strength (Mpa)	Variation	% Variation
1	NS 123:2041	OPC 43 Grade	3 Days	43.51	–	–
			7 Days	51.04	–	–
			28 Days	55.28	–	–
		PPC	3 Days	23.19	–	–
			7 Days	33.93	–	–
			28 Days	45.10	–	–
2	ASTM C109/109M	OPC 43 Grade	3 Days	41.62	-1.89	-4.34
			7 Days	48.7	-2.34	-4.58
			28 Days	52.75	-2.53	-4.58
		PPC	3 Days	21.38	-1.81	-7.81
			7 Days	30.17	-3.76	-11.08
			28 Days	39.39	-5.71	-12.66
3	ISO 679:2009	OPC 43 Grade	3 Days	39.51	-4	-9.19
			7 Days	44.32	-6.72	-13.17
			28 Days	49.51	-5.77	-10.44
		PPC	3 Days	20.11	-3.08	-13.28
			7 Days	28.26	-5.67	-16.71
			28 Days	36.84	-8.26	-18.31
4	BS EN 196-1:2016	OPC 43 Grade	3 Days	39.51	-4	-9.19
			7 Days	44.32	-6.72	-13.17
			28 Days	49.51	-5.77	-10.44
		PPC	3 Days	20.11	-3.08	-13.28
			7 Days	28.26	-5.67	-16.71
			28 Days	36.84	-8.26	-18.31

Table 03: Comparative Variation in Test Results

S.N.	Cement Type	Testing Period	Compressive Strength (Mpa)		NS Vs ASTM (%)	NS Vs ISO (%)
1	OPC 43G	3 Days	43.51	–	4.54	10.12
		7 Days	51.04	–	4.80	15.16
		28 Days	55.28	–	4.80	11.65
	PPC	3 Days	23.19	–	8.47	15.32
		7 Days	33.93	–	12.46	20.06
		28 Days	45.10	–	14.50	22.42
2	OPC 43G	3 Days	41.62	1.89
		7 Days	48.7	2.34
		28 Days	52.75	2.53
	PPC	3 Days	21.38	1.81
		7 Days	30.17	3.76
		28 Days	39.39	5.71
3	OPC 43G	3 Days	39.51	4
		7 Days	44.32	6.72
		28 Days	49.51	5.77
	PPC	3 Days	20.11	3.08
		7 Days	28.26	5.67
		28 Days	36.84	8.26
4	OPC 43G	3 Days	39.51	4
		7 Days	44.32	6.72
		28 Days	49.51	5.77
	PPC	3 Days	20.11	3.08
		7 Days	28.26	5.67
		28 Days	36.84	8.26

The above table shows that the test method developed by NBSM gives a higher value of compressive strength of hydraulic cement than other recognized international standards which means NS 123:2041 allows the use of weaker cement in quality assessment and monitoring. This difference in compressive strength is greater in Portland pozzolana cement in comparison with ordinary Portland cement. Among the international standards taken into consideration in this research, ISO 679:2009 and BS EN 196 – 1:2016 provides more relevant test result according to the concrete exposure environment of Nepal. NS 123: 2041 test method provides 4.80% more strength than ASTM C109 and 11.65% more strength than ISO 679:2009 for ordinary Portland cement. Similarly, it provides 14.50% more compressive strength than ASTM C109 and 22.42% more strength than ISO 679:2009 for Portland Pozzolana Cement. The variation in compressive strength of hydraulic cement due to curing temperature variations is analyzed by numerous laboratory tests and comprehensive data processing. Large number of cement samples of various brands was tested to determine the compressive strength of respective samples at varying curing temperatures. The test result of these experiments gives valuable insights into the strength development pattern and trend of hydraulic cement in varying curing temperatures that help to quantify the variation in test methods and their impacts on concrete structures. The compressive strength variation due to varying curing temperatures of hydraulic cement directly impacts the load-carrying capacity and the serviceability capacity of the concrete structure according to the temperature of the exposure environment. The compressive strength of pozzolana cement is greatly influenced by cold exposure which impairs the primary function of cement in concrete structures. This research shows that strength development in hydraulic cement in cold weather is very slow which lengthens the stripping time of concrete structure and an added quantity of cement might be required for the same design strength of structure which ultimately leads to the cost overruns of the projects. There are many national and international standards for the determination of physical characteristics of hydraulic cement including compressive strength which recommends the curing water temperature that does not really simulate the real exposure environment of the structure causing poor-quality control over cement manufacturing and filed applications. According to the laboratory experiments of this research physical parameter test method of hydraulic cement followed by Nepal which is developed by NBSM is weaker than international standards taken into consideration in this research i.e., ASTM C109, ISO 679:2009 and BS EN 196 – 1: 2016. To analyze the variation in compressive strength of hydraulic cement due to curing temperature variation numerous laboratory test was conducted which yielded significant findings that shed light on the relationship between curing temperature and the compressive strength of hydraulic cement. This research confirmed a statistically significant relationship between curing temperature and compressive strength. Specifically, as the curing temperature decreased, the compressive strength of hydraulic cement tended to decrease as well which reduction is more prominent in Portland pozzolana cement. The strength of the relationship between curing temperature and compressive strength was substantial, with a correlation coefficient indicating a very strong positive correlation. This suggests that careful control and manipulation of curing temperature in laboratory tests can have a pronounced impact on the quality and performance of hydraulic cement.

5 CONCLUSION

In conclusion, the research has provided valuable insights into the critical relationship between curing temperature and the compressive strength of hydraulic cement. Several key findings from this study improve our understanding of hydraulic cement performance and its practical applications. This study’s main finding is that curing temperature directly and statistically significantly affects compressive strength. It is well known that hydraulic cement compressive strength increases with curing temperature. This positive correlation emphasises the importance of precise temperature control in laboratory tests to simulate concrete structure exposure. In comparison to standard strength (55 MPa) at 27°C, the compressive strength of ordinary Portland cement is decreased up to 41 MPa at 5°C, 25.46% less than standard strength, and up to 24 MPa, 46.27% less than standard strength of 45 MPa for pozzolana cement. This makes design strength achievement in cold weather difficult and stripping time longer. At 40°C curing temperature, ordinary Portland cement’s compressive strength increases by 17.16% from 55 MPa and 14.83% for pozzolana cement of 45 MPa. The regression model of this laboratory data shows a 0.99 correlation between compressive strength and curing temperature. Ordinary Portland and Portland pozzolana cement strength development trends and patterns are also important. The study found that pozzolana cement has a 46.27 percent compressive strength variation compared to 25.46% for Portland cement. The compressive strength of PPC cement decreases by 8.80% at 25°C, 2°C below standard, but increases by 5.03% at 30°C, 3°C above standard, meaning strength decrement is greater than strength increase. This strength decrease becomes more noticeable over time, but the strength increment at higher curing temperatures gradually decreases. Pozzolana cement strength development is strongly influenced by curing water temperature. Last, the study found that the NS 123:2041 test method consistently produces higher compressive strength results than other international standards. The compressive strength of PPC cement at ASTM C109 curing temperature is 39.39 MPa and 45.10 MPa at NS 123:2041, 14.50% higher than ASTM C109. NS 123:2041 yields 14.50% more compressive strength than ASTM C109 and 22.42% more than ISO 679:2009 and BS EN 196 – 1:2016, causing quality control and performance monitoring to vary greatly. This emphasises the importance of standardising cement compressive strength testing to ensure accuracy and consistency. Overall, these findings offer construction and cement manufacturing industry guidance. This knowledge can help engineers and researchers choose curing temperatures, cements, and testing methods to build more reliable and durable concrete structures.

6. RECOMMENDATION

Based on the findings several key recommendations emerge that can inform practices in the construction industry and cement manufacturing. These recommendations are aimed at optimizing the performance and quality of hydraulic cement:

1. Use a temperature monitoring and regulation system to maintain consistent and controlled curing conditions that directly influence the compressive strength of hydraulic cement.
2. Recognize that different cement types respond differently to curing temperature variations. While selecting cement for specific applications, consider the anticipated exposure conditions and compressive strength test method.
3. Ensure that testing laboratories adhere to standardized procedures to maintain consistency and accuracy in compressive strength assessments and that the curing temperature aligns with the average temperature of the exposure environment.
4. Special care should be taken for the stripping time of structures exposed to cold weather, this special measure should be added to the national code or standards.
5. The curing temperature recommended by NS 123:2041 does not represent the average atmospheric temperature of all regions of Nepal so a curing regime for different regions or region-wise temperature adjustment should be introduced in NS 123: 2041.
6. Encourage further research in this field to explore additional variables and their interactions with curing temperature. Investigate the influence of cement composition, admixtures, and other additives on compressive strength under varying curing conditions. Evaluate the long-term performance and durability of hydraulic cement exposed to varying curing conditions.
7. By implementing these recommendations, the construction industry, cement manufacturers and regulatory bodies can enhance the reliability and quality of cement-based structures while optimizing resource utilization. Moreover, continued research and collaboration within the field will contribute to the development of more robust and sustainable construction practices, ultimately benefitting both industry professionals and the broader community.

REFERENCES

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