What is Concrete?[1]

Concrete is the most used construction material in the world

In a broad sense, a substance formed through the utilization of an adhesive [2] is referred to as concrete. Typically, this adhesive substance originates from the chemical reactionbetween hydraulic cement [3] and water.However, this rudimentary definition encompasses a diverse array of concretes, encompassing those incorporating various types of cement, concretes integrating pozzolanssuch as fly ash[4],iron smelting furnace slag[5],and silica fume[6].Additionally, it includes concretes incorporating additives[7],recycled aggregates[8],polymers[9],[10]and fibers.[11]Such concretes may undergo diverse treatments, including exposure to heat, steam,[12]high-pressure processing (autoclave),[13]and vacuum,[14] among other methods.

Presently, the breadth of this domain has expanded considerably owing to noteworthy advancements in the concrete industry. Its versatility now encompasses a diverse spectrum of concepts, including structural lightweight concrete,[15]heavyweight concrete,[16]high-strength and ultra-high-strength concrete,[17]durable and exceptionally robust concrete,[18]self-compacting concrete,[19]concrete endowed with shrinkage compensation properties,[20]mass concrete,[21]roller-compacted concrete,[22] and various other forms contribute to the broad and dynamic realm of this essential construction material.

The Historical Evolution of Cement and Concrete Usage:

Cement, a fundamental constituent of concrete, traces its origins back approximately 12 million years. Formed through the chemical reaction between limestone and oil-bearing rock in what is now Israel. these naturally occurring sediments containing cement compounds were unearthed and recognized by geologists during the 60s and 70s of the 20th century.

The earliest structures resembling concrete were constructed around 6500 BC by the Nabataeans and Bedouins in southern Syria and northern Jordan. Moving forward to approximately 5600 BC, residences with concrete floors emerged along the Danube River in regions that once comprised the former Yugoslavia. By 3000 BC, ancient Egyptians utilized a blend of mud and straw, creating a mixture akin to cement mortar, to construct the triple pyramids. The Great Pyramid of Egypt alone utilized about 500,000 tons to interlock the stones. Concurrently, the Chinese employed a cement-type material for boat construction and the Great Wall of China

 

Around 600 BC, the Greeks stumbled upon natural pozzolan with hydraulic properties when combined with lime. However, it was the Romans who harnessed this discovery to its fullest potential in their constructions. The Pantheon, finalized by Emperor Hadrian in 125 AD, stands as the largest unreinforced concrete dome ever constructed. Following the fall of the western Roman Empire in 476 AD and persisting into the Middle Ages, the methodology for producing pozzolanic cement remained shrouded in mystery. It wasn’t until 1414 that manuscripts detailing the production of this cement type were unearthed, reigniting interest in this construction material.

Cement technology experienced significant advancement in 1793 following John Smeaton’s breakthroughs[23] in producing cement clinker[24] through the calcination of limestone-containing clay. Smeaton employed this material in the historical restoration of the Eddystone lighthouse[25]in Cornwall,[26] England.

Finally, Joseph Aspdin pioneered today’s[27] Portland cement in 1824[28] by firing gypsum powder and clay in a kiln. The nomenclature “Portland cement” was attributed to its resemblance to the building stones of the Portland region in England. In 1891, George Bartholomew constructed the first concrete street[29] in Bellefontaine, Ohio,[30] which remains in service to this day.

For a deeper dive into these historical cases, refer to the article “Concrete History.”

Concrete Components and their Interplay:

Concrete, in its essence, is crafted through the amalgamation of cement, water, and aggregate, with the potential inclusion of additives. A pivotal query that arises pertains to the relationship and proportionality of these Components. Addressing this inquiry involves consideration from three distinct perspectives:

The first perspective positions the binder, the output of [31], as the primary Component of concrete. In this view, aggregates assume the role of a cost-effective filler within the mixture.

The second perspective posits that [32] functions as a diminutive construction material amalgamated with mortar, itself a combination of hydrated cement and [33].

The third perspective, akin to the first, conceives concrete as comprising two phases: hydrated cement paste and aggregate. Consequently, the concrete’s properties are a derivative of the characteristics inherent in these two components and their interplay.

The second and third perspectives are deemed more favorable for elucidating concrete behavior, with the first perspective, grounded in the filling properties of aggregates, being less pertinent. If hypothetically, the cost of cement becomes lower than that of aggregate, thus removing the cheapness of aggregate from the conversation, can cement and water alone serve as viable construction materials?

The unequivocal response to the aforementioned query is negative.[34] This is attributable to factors such as the significantly greater volume changes and[35] increased shrinkage[36] and creep of hydrated cement paste compared to[37] concrete. Furthermore, the substantial heat generated by the extensive volume of hydrated cement, particularly in hot weather conditions, contributes to cracking.[38] Additionally, empirical observations affirm that aggregates exhibit greater resistance to chemical attacks than cement paste. Consequently, transcending considerations of price and cost, the incorporation of aggregate in concrete is deemed advantageous.

 

Implementation of Knowledge in Concrete Production:

Concrete stands as the most extensively utilized material globally, and as such, understanding how to define “good concrete” becomes paramount amid the myriad topics at hand. It is imperative, however, to initially delineate ” bad and poor-quality concrete,” which regrettably represents the prevailing form of construction material. Imagine a soup-like blend solidifying into a weak, uneven mass marred by unsightly[39] honeycomb holes. Strikingly, both good and bad concrete share parentage—cement, water, and aggregate. The differentiating factor? The masterful touch—knowledge and[40]a nuanced understanding of implementation.

Addressing the discourse on knowledge in ready-mixed concrete production, two overarching criteria for assessing good concrete emerge. These criteria encompass ensuring requisite conditions in the two states of “fresh concrete” and[42]“hardened concrete.”[43]Fresh concrete requirements necessitate an optimal consistency for compaction using standard workshop equipment[44] and adequate viscosity[45] for conveyance and concreting[46] without[47] segregation. Regarding hardened concrete, the provision of compressive strength is typically imperative,[48] , as it is easy to measure. While the compressive strength test result does not singularly ascertain the intrinsic strength of concrete, it serves as a test for its quality. Consequently, compressive strength stands as a robust indicator to validate concrete conformity with guidelines and contractual stipulations.

Compressive strength mirrors certain properties and attributes of concrete,[49]including density,[50]impermeability,[51]durability,[52]abrasion resistance,[53]impact resistance,[54]tensile strength, and sulfate resistance,[55] etc among others. However, essential characteristics such as shrinkage and creep lie beyond the purview of compressive strength. Notably, these attributes are not exclusively contingent on compressive strength;[56] water/cement ratio or cement grade[57] may exert influence. However, from a holistic perspective, concretes exhibiting higher compressive strength generally manifest more favorable characteristics and specifications.

Concrete properties are not solely contingent on the attributes of their components[58] but also hinge on the interface (distance) between them[59] and their interactive dynamics. To comprehend this concept, it is crucial to recognize that the volume of well-compacted fresh concrete exceeds the compacted volume of its aggregate components by about 3% or more. This discrepancy arises from the fact that the aggregates in concrete are not interconnected point-to-point; rather, a thin layer of cement paste delineates them.[60] This thin layer is termed the Interfacial Transition Zone (ITZ) between the cement paste and aggregate.

A consequential insight from this observation is that the mechanical properties of concrete, such as rigidity, cannot be directly correlated to the mechanical properties of aggregates.[61]Instead, they hinge on the unique properties of each aggregate and the[62] concrete structure. Another insight pertains to the modulus of elasticity,[63] wherein individual aggregates and hydrated cement paste[64] exhibit a linear stress-strain relationship. However, their amalgamation yields a curvilinear relationship due to microcracks developing in the[65]Transition Zone under loading. The proliferation of these microcracks escalates local stress intensity and strain magnitude, causing the strain to increase at a faster rate than the stress, thereby initiating a bending in the stress-strain diagram.

Steel or Concrete? T hat is the question!

How is concrete, seemingly inferior in strength and hardness compared to steel is the most widely employed engineering material? The reasons can be summarized as follows:

• Diverging from ordinary wood and steel, concrete boasts remarkable water resistance, rendering it an ideal material for constructing water monitoring, storage, and transfer facilities. Notably, some of humanity’s oldest structures, including waterways[66]and dams dating back[67]to the Roman period, were fashioned using a rudimentary form of concrete The resilience of concrete in corrosive environments, such as coastal areas, were fashioned using a rudimentary form of concrete[68] stands as an additional catalyst for the prevalent use of this construction material.
• The malleability of fresh concrete allows for the creation of diverse shapes. Employing molds with varying geometries addresses both structural and architectural requirements. This adaptability contributes to the widespread applicability of concrete in construction.
• With lower corrosion potential compared to steel, concrete requires easier and more affordable maintenance.
• This attribute enhances its longevity and reduces upkeep costs.
• Concrete exhibits heightened resilience to cyclic loading and fatigue in contrast to steel.
• This [69] positions concrete as a preferred choice in scenarios where enduring [70] under repeated stress is imperative.

The Future Challenges for Concrete Industries:

Change is inevitable, yet the pace and abruptness of transformative developments can be markedly disruptive. Presently, we confront economic and environmental challenges stemming from factors such as population growth, urbanization, and the ramifications of technology. While these elements are interconnected, each warrants separate examination to enhance our understanding of their historical impacts and facilitate more accurate predictions for the future.

• Population Growth: In the early 20th Century, the global population stood at approximately 1.5 billion people, a figure that escalated to 6 billion by the Century’s end. It is noteworthy that the journey from 1.5 to 6 billion transpired within a mere hundred years, contrasting sharply with the 10,000 years required for the world’s population to reach 1.5 billion following the last ice age. This demographic explosion necessitates extensive infrastructure development, with construction in which concrete is an integral component, constituting a critical need.
• Urbanization: Statistics reveal a direct correlation between population growth and the escalating trend of urbanization. In the early 20th Century, roughly 10% of the global populace resided in cities, a percentage that surged to 50% at the outset of the 21st Century. Consequently, the expansion of cities and urban infrastructures must exhibit commensurate growth to meet the demands of this transformative urban landscape.
• Technology and its Environmental Impacts: Both population growth and urbanization exert profound influences on the energy, production, and transportation sectors. Regrettably, our technological decisions are often based on short-term considerations with narrowly defined objectives, neglecting the long-term consequences of these choices. A study conducted at the beginning of the 21st Century by Hawken et al.[72] revealed that a mere 6% of the total global material flow, exceeding 500 billion tons annually, culminates in consumer products. The remaining raw materials revert to nature in the form of solid, liquid, or gaseous wastes, posing environmental hazards.

Environmental Pollution: Environmental pollution, though not a novel concern, has evolved from regional to global dimensions. Contemporary scientists contend that the most pressing environmental challenge is human-induced climate change, which has led to global warming over the past Century due to increased greenhouse gas concentrations in the Earth’s atmosphere. Consequently, since 1990, a considerable number of severe weather events have been documented across the globe. I n tandem with the depletion of natural resources, the quality of the environment—critical for sustaining life and fostering sustainable development—is also in decline.

Conventional concrete typically comprises 12% cement, 8% water, and 80% aggregate by mass. These proportions translate to the global consumption of 1.5 billion tons of cement, 9 billion tons of sand, and 1 billion tons of water in concrete production. This industry, amounting to 11.5 billion tons, stands as the largest consumer of natural resources globally and is projected to escalate to 16-18 billion tons annually by 2050. Examining these figures leads to the conclusion that the extraction, refinement, and transportation of such substantial materials, coupled with the energy-intensive production processes, significantly impact the ecological balance of regions.

While concrete made from Portland cement is commonly perceived as environmentally friendlier than alternative building materials, it is imperative to address and mitigate the environmental impact of the concrete industry. Portland cement, the primary hydraulic component of concrete, is notably energy-intensive, requiring 4 gigajoules of energy per ton of cement, and concurrently emits substantial carbon dioxide during production. The production of one ton of Portland cement clinker releases approximately one ton of carbon dioxide, contributing to nearly 7% of global carbon dioxide emissions from the production of 1.5 billion tons of cement annually.

Two overarching approaches can be employed to address the environmental effects of the concrete industry. The long-term strategy involves reducing the rate of concrete consumption, though this is impractical, particularly given the ongoing global development and the continued demand for this essential material. Alternatively, the use of industrial ecology, which emphasizes the incorporation of[73] recycled and alternative materials, presents a viable solution. This involves appropriately recycling demolished materials, utilizing wastewater and non-potable water, and substituting a portion of cement with pozzolans such as fly ash, blast furnace slag, silica fume, and zeolite, among others.

In summary, the short-term focus for reducing carbon dioxide emissions involves two primary strategies: diminishing clinker content in the final cement product through maximum utilization of mineral additives and incorporating blended cement[74] in concrete production. Fly ash exhibits the most promising potential for curbing greenhouse gas emissions among mineral additives. Based on Jaren’s research,[75]fly ash is anticipated to emerge as the most potent tool for fostering sustainable development in the concrete industry over the next two decades.

Durability of Concrete and its Implications for Sustainable Development:

In the context of the previously mentioned industrial ecosystem cases, it becomes evident that addressing the sustainable development of the concrete industry through short-term solutions is only a partial remedy. Long-term sustainable development necessitates substantial advancements in resource efficiency. It is evident that extending the service life of concrete and concrete structures will have a profound impact on diminishing the resource consumption inherent in this industry.

An essential question emerges: What is the timeframe available to transform the concrete industry and align it with the principles of sustainable development, considering the imminent risk of reaching irreparable and irreversible global climate conditions and depletion of natural resources?

(Mehta, P.K., Concr. Int., Vol. 24, No. 7, pp. 23–28, July 2002.)

Current global population forecasts indicate stabilization in Europe and North America, with declining population growth rates observed in Asia, Africa, and South America. Experts anticipate that the world’s population will burgeon to approximately 9-10 billion people by 2050 before entering a stabilization phase. Given the direct correlation between population growth and urbanization, it is estimated that nearly three-quarters of this population will reside in urban areas.

Based on the present rate of concrete consumption, projections suggest that annual consumption could surge to 16 billion tons by 2050. Subsequently, applying industrial ecology principles in industries and construction, coupled with advancements in structural durability, is expected to prompt a downward trajectory. Consequently, the perspective of sustainable development within the concrete industry is envisaged as a transformative movement in the coming Century. Throughout the past Century, various facets of the concrete industry have successfully surmounted obstacles and challenges, positioning themselves as integral contributors to an overarching initiative striving to enhance the industry’s environmental sustainability.

The Final Conclusion:

In conclusion, concrete emerges as the most extensive man-made product, embodying a tripartite composition comprising cement paste, aggregate, and the transition zone between the cement paste and aggregate. Only the aggregate remains constant among these three constituent phases, while the other two phases undergo changes and development over time. Only the aggregate remains constant among these three constituent phases, while the other two phases undergo changes and development over time. This dynamic nature is reflected in the etymology of the English term “concrete,” derived from the Latin root “Concretus,” signifying growth. Notably, aside from cement, water, and aggregate, air also constitutes a concrete structure component.

Challenge your knowledge and seek improvement!

To delve deeper into the subject matter, explore the following inquiries:

1. 1. In the context of concrete, is the Transition Zone stronger or weaker compared to the mass of cement paste? What factors contribute to this strength or weakness?
2. 2. What is the optimal ratio of constituent components in well-constructed concrete? Can achieving the correct proportion of components guarantee the production of “good concrete”?
3. 3. How is the durability of concrete defined, and what characteristics contribute to a concrete structure’s extended lifespan?

Reference

• Burrows, R.W., The Visible and Invisible Cracking of Concrete, ACI Monograph No. 11, p. 78,
• Corinaldesi, V., and G. Moricani, ACI SP-199, American Concrete Institute, Farmington Hills, MI, pp. 869–884, 2001.
• Gjerde, T., Nordisk Betong (Stockholm), No. 2–4, pp. 95–96, 1982.
• Hawken, P., E. Lovins, and H. Lovins, Natural Capitalism—Creating the Next Industrial Revolution, Boston, Little Brown, p. 369, 1999.
• Jahren, P., Greener Concrete—What are the Options? SINTEF Report No. STF-A03610, p. 84, 2003.
• Mehta P.K., and P.J.M. Monteiro, Concrete: Microstructure, Properties and Materials, 4^th McGraw-Hill, New York, 2014.
• Mehta, P.K., and R.W. Burrows, Building Durable Structures in the 21st Century, Int., Vol. 23, No. 3, pp. 57–63, 2001.
• Mehta, P.K., Int., Vol. 24, No. 7, pp. 23–28, 2002.
• Neville A.M., Properties of Concrete, 5^th Pearson, Harlow, England, 2011.
• Neville A.M., and J.J. Brooks, Concrete Technology, 2^nd Prentice Hall, Pearson, Harlow, England, 2010.
• Wilson, E.O., Consilience: The Unity of Knowledge, Alfred Knof, New York, p. 325, 1998.
• https://www.cement.org
• https://www.nrmca.org
• https://www.concrete.org
• https://www.rilem.net

[1] Concrete

[2] Cementing Medium

[3] Hydraulic Cement

[4] Pozzolan

[5] Fly Ash

[6] Blast-Furnace Slag

[7] Microsilica

[8] Admixtures

[9] Recycled Aggregates

[10] Polymer

[11] Fibre

[12] Steam-Curing

[13] Autoclaving

[14] Vacuum-Treating

[15] Structural Lightweight Concrete

[16] Heavyweight Concrete

[17] High & Ultra High Strength Concrete

[18] High & Ultra High-Performance Concrete

[19] Self-Consolidating Concrete

[20] Shrinkage-Compensating Concrete

[21] Mass Concrete

[22] Roller-Compacted Concrete

[23] John Smeaton

[24] Clinker

[25] Eddystone Lighthouse

[26] Cornwall

[27] Joseph Aspdin

[28] Portland

[29] Bellefontaine, Ohio

[30] George Bartholomew

[31] Hydration

[32] Coarse Aggregate

[33] Fine Aggregate

[34] Volume Changes

[35] Shrinkage

[36] Creep

[37] Cracking

[38] Chemical Attack

[39] Honeycombed Voids

[40] Know-How

[41] Three Gorges Dam

[42] Fresh Concrete

[43] Hardened Concrete

[44] Cohesiveness

[45] Transporting

[46] Placing

[47] Segregation

[48] Compressive Strength

[49] Density

[50] Impermeability

[51] Durability

[52] Resistance to Abrasion

[53] Resistance to Impact

[54] Tensile Strength

[55] Resistance to Sulphates

[56] Water/Cement Ratio

[57] Cement Content

[58] Interface

[59] Interactions

[60] Interfacial Transition Zone

[61] Rigidity

[62] Matrix

[63] Modulus of Elasticity

[64] Stress-Strain Relation

[65] Microcrack

[66] Aqueduct

[67] Waterfront Retaining Walls

[68] Corrosive Environments

[69] Cyclic Loadings

[70] Fatigue

[71] Precast

[72] Hawken et al.

[73] Industrial Ecology

[74] Blended Cements

[75] Jahren

[76] Portland Cement Association (Cement.org)