WEBVTT 1 00:00:01.879 --> 00:00:06.559 Welcome to the I Can't Sleep Podcast, where I help 2 00:00:06.599 --> 00:00:11.480 you drift off one fact at a time. I'm your host, 3 00:00:11.640 --> 00:00:21.000 Benjamin Boster, and today's episode is about concrete. Concrete is 4 00:00:21.039 --> 00:00:26.839 a composite material composed of aggregate bound together with a 5 00:00:26.839 --> 00:00:33.000 fluid cement that cures to a solid. It is the 6 00:00:33.079 --> 00:00:38.759 second most used substance after water, the most widely used 7 00:00:38.799 --> 00:00:46.200 building material, and the most manufactured material in the world. 8 00:00:47.039 --> 00:00:51.280 When aggregate is mixed with dry Portland cement and water, 9 00:00:52.600 --> 00:00:56.240 the mixture forms a fluid slurry that can be poured 10 00:00:56.320 --> 00:01:01.200 and molded into shape. The cement reys with the water 11 00:01:01.399 --> 00:01:06.760 through a process called hydration, which hardens it after several 12 00:01:06.840 --> 00:01:12.280 hours to form a solid matrix that binds the materials 13 00:01:12.319 --> 00:01:17.599 together into a durable, stone like material with various uses. 14 00:01:20.920 --> 00:01:26.439 This time allows concrete to not only be cast in forms, 15 00:01:26.480 --> 00:01:30.400 but also to have a variety of tooled processes performed. 16 00:01:33.200 --> 00:01:39.359 The hydration process is exocermic, which means that ambient temperature 17 00:01:39.519 --> 00:01:43.280 plays a significant role in how long it takes concrete 18 00:01:43.319 --> 00:01:50.239 to set. Often, additives are included in the mixture to 19 00:01:50.319 --> 00:01:55.519 improve the physical properties of the wet mix, delay or 20 00:01:55.879 --> 00:02:05.359 accelerate the curing time, or otherwise the finished material. Most 21 00:02:05.400 --> 00:02:10.639 structural concrete is poured with reinforcing materials such as steel 22 00:02:10.719 --> 00:02:21.199 rebar embedded to provide tensile strength yielding reinforced concrete. Before 23 00:02:21.240 --> 00:02:25.000 the invention of Portland cement in the early eighteen hundreds, 24 00:02:26.080 --> 00:02:31.280 lime based cement binders such as lime putty were often used. 25 00:02:33.199 --> 00:02:37.960 The overwhelming majority of concretes are produced using Portland cement, 26 00:02:39.240 --> 00:02:45.280 but sometimes with other hydraulic cements such as calcium luminate cement. 27 00:02:47.639 --> 00:02:53.319 Many other non cementitious types of concrete exist with other 28 00:02:53.439 --> 00:02:59.919 methods of binding aggregate together, including asphalt concrete with a 29 00:03:00.039 --> 00:03:05.759 bitumen binder, which is frequently used for road surfaces, and 30 00:03:06.039 --> 00:03:13.800 polymer concretes that use polymers as a binder. Concrete is 31 00:03:13.960 --> 00:03:20.000 distinct from mortar. Whereas concrete is itself a building material 32 00:03:20.800 --> 00:03:28.039 and contains both coarse, large and fine small aggregate particles, 33 00:03:28.199 --> 00:03:33.280 mortar contains only fine aggregates and is mainly used as 34 00:03:33.319 --> 00:03:37.599 a bonding agent to hold bricks, tiles, and other masonry 35 00:03:37.680 --> 00:03:45.520 units together. Grout is another material associated with concrete and cement. 36 00:03:47.240 --> 00:03:52.159 It also does not contain coarse aggregates and is usually 37 00:03:52.400 --> 00:03:57.680 either poorable or a sixotropic and is used to fill 38 00:03:57.800 --> 00:04:04.439 gaps between masonry components or coarse aggregate which has already 39 00:04:04.479 --> 00:04:11.840 been put in place. Some methods of concrete manufacture and 40 00:04:11.879 --> 00:04:16.680 repair involve pumping grout into the gaps to make up 41 00:04:16.720 --> 00:04:24.879 a solid mass in situ. The word concrete comes from 42 00:04:24.920 --> 00:04:31.399 the Latin word concretis, meaning compact or condensed. The perfect 43 00:04:31.519 --> 00:04:38.319 passive participle of concrescere from cone together and cressere to grow. 44 00:04:43.240 --> 00:04:47.519 Concrete floors were found in the Royal Palace of Tirans, Greece, 45 00:04:48.600 --> 00:04:52.680 which dates roughly to fourteen hundred to twelve hundred BC. 46 00:04:55.399 --> 00:04:59.480 Lime mortars were used in Greece, such as in crete 47 00:04:59.519 --> 00:05:04.839 and cip press. In eight hundred b C. The Assyrian 48 00:05:04.959 --> 00:05:09.720 Jiwan Aqueduct six eighty eight b C made use of 49 00:05:09.879 --> 00:05:18.279 waterproof concrete. Concrete was used for construction in many ancient structures. 50 00:05:20.839 --> 00:05:26.360 Small scale production of concrete like materials was pioneered by 51 00:05:26.399 --> 00:05:30.680 the Nebataean traders, who occupied and controlled a series of 52 00:05:30.720 --> 00:05:35.360 oaysees and developed a small empire in the regions of 53 00:05:35.480 --> 00:05:40.439 southern Syria and northern Jordan from the fourth century b C. 54 00:05:43.360 --> 00:05:48.439 They discovered the advantages of hydraulic lime with some self 55 00:05:48.480 --> 00:05:55.079 cementing properties. By seven hundred b C. They built kilns 56 00:05:55.160 --> 00:05:59.600 to supply mortar for the construction of rubble masonry houses, 57 00:06:00.519 --> 00:06:09.120 concrete floors, and underground waterproof cisterns. They kept the cistern secret, 58 00:06:09.240 --> 00:06:12.839 as these enabled the Naboteans to thrive in the desert. 59 00:06:14.680 --> 00:06:22.360 Some of these structures survived to this day. The Romans 60 00:06:22.480 --> 00:06:27.639 used concrete extensively from three hundred b C to eighty 61 00:06:27.680 --> 00:06:35.079 four seventy six during the Roman Empire. Roman concrete was 62 00:06:35.160 --> 00:06:43.040 made from quicklime, pozzolana and an aggregate of pumice. Its 63 00:06:43.120 --> 00:06:48.040 widespread use in many Roman structures, a key event in 64 00:06:48.120 --> 00:06:53.800 the history of architecture, termed the Roman architectural Revolution, freed 65 00:06:53.920 --> 00:07:01.199 Roman construction from the restrictions of stone and brick materials. 66 00:07:01.240 --> 00:07:06.240 It enabled revolutionary new ideas in terms of both structural 67 00:07:06.319 --> 00:07:12.680 complexity and dimension. The Colosseum in Rome was built largely 68 00:07:12.720 --> 00:07:17.959 of concrete, and the Pantheon was the world's largest unreinforced 69 00:07:18.079 --> 00:07:24.879 concrete dome. Concrete, as the Romans knew it, was a 70 00:07:24.920 --> 00:07:30.839 new and revolutionary material, laid in the shape of arches, vaults, 71 00:07:30.879 --> 00:07:36.439 and domes. It quickly hardened into a rigid mass, free 72 00:07:36.680 --> 00:07:40.680 from many of the internal thrusts and strains that troubled 73 00:07:40.680 --> 00:07:48.360 the builders of similar structures in stone or brick. Modern 74 00:07:48.439 --> 00:07:53.319 tests show that OPA's sementissium had a similar compressive strength 75 00:07:53.480 --> 00:07:59.720 to modern Portland cement concrete. However, due to the absence 76 00:07:59.759 --> 00:08:05.000 of reinforcement, its tensile strength was far lower than modern 77 00:08:05.040 --> 00:08:13.519 reinforced concrete, and its mode of application also differed. Modern 78 00:08:13.639 --> 00:08:21.040 structural concrete differs from Roman concrete in two important details. First, 79 00:08:21.560 --> 00:08:26.720 its mixed consistencies fluid and homogeneous, allowing it to be 80 00:08:26.759 --> 00:08:31.399 poured into forms rather than requiring hand layering, together with 81 00:08:31.639 --> 00:08:37.600 the replacement of aggregate, which in Roman practice often consisted 82 00:08:37.639 --> 00:08:46.000 of rubble. Second, integral reinforcing steel gives modern concrete assemblies 83 00:08:46.120 --> 00:08:51.960 great strengths and tension, whereas Roman concrete could depend only 84 00:08:52.039 --> 00:08:55.960 upon the strength of the concrete bonding to resist tension. 85 00:09:00.320 --> 00:09:05.600 The long term durability of Roman concrete structures was found 86 00:09:05.600 --> 00:09:09.679 to be due to the presence of pyroclastic volcanic rock 87 00:09:09.799 --> 00:09:16.200 and ash in a concrete mix. The crystallization of stretlinge 88 00:09:16.440 --> 00:09:20.600 during the formation of the concrete, and its merging with 89 00:09:20.720 --> 00:09:26.639 similar calcium aluminum silicate hydrate structures helped gives a Roman 90 00:09:26.720 --> 00:09:34.559 concrete a greater degree of fracture resistance compared to modern concrete. 91 00:09:34.879 --> 00:09:40.000 In addition, Roman concrete is significantly more resistant to erosion 92 00:09:40.080 --> 00:09:46.639 by sea water than modern concrete. The aforementioned pyroclastic materials 93 00:09:47.399 --> 00:09:51.559 react with sea water to form aluminium to bermeerite crystals 94 00:09:51.600 --> 00:09:57.960 over time. The use of hot mixing in preparation of concrete, 95 00:09:58.480 --> 00:10:02.080 leading to the formation of light class in the final product, 96 00:10:03.080 --> 00:10:06.279 has been proposed to give the Roman concrete a self 97 00:10:06.320 --> 00:10:13.840 healing ability. The widespread use of concrete in many Roman 98 00:10:13.919 --> 00:10:20.840 structures ensured that many survive to the present day. The 99 00:10:20.879 --> 00:10:27.039 baths of Caracalla and Rome are just one example. Many 100 00:10:27.159 --> 00:10:31.840 Roman aqueducts and bridges, such as the magnificent Pont Nouguer 101 00:10:32.639 --> 00:10:37.799 and Southern France, have masonry cladding on a concrete core, 102 00:10:39.039 --> 00:10:46.320 as does the dome in the Pantheon In Britannia. After 103 00:10:46.360 --> 00:10:50.399 the Roman Empire, there is evidence of the continued use 104 00:10:50.559 --> 00:10:54.720 of burned lime, and remains of an eighth century mortar 105 00:10:54.799 --> 00:10:59.440 mill have been found in Northamptonshire, but it is thought 106 00:10:59.559 --> 00:11:04.039 that low kiln temperatures in the burning of lime, lack 107 00:11:04.159 --> 00:11:09.840 of pozzolana, poor mixing, and an Anglo Saxon culture of 108 00:11:10.000 --> 00:11:14.759 timber construction all contributed to a decline in the quality 109 00:11:14.799 --> 00:11:18.519 of concrete and mortar there, but it did not become 110 00:11:18.600 --> 00:11:24.919 a lost art. From the eleventh century in England, the 111 00:11:25.039 --> 00:11:30.480 increased use of stone and church in castle construction led 112 00:11:30.519 --> 00:11:36.240 to an increased demand for mortar. Quality began to improve 113 00:11:36.279 --> 00:11:42.840 in the twelfth century threw better grinding and seeving. Medieval 114 00:11:42.919 --> 00:11:47.759 lime mortars and concretes were non hydraulic and were used 115 00:11:47.799 --> 00:11:56.840 for binding masonry, parting, binding rubble masonry, cores and foundations. 116 00:11:58.320 --> 00:12:05.960 Bartolomeus Anglicu, in his De Proprietatibus Rerum twelve forty describes 117 00:12:06.159 --> 00:12:11.679 the making of mortar. In an English translation from thirteen 118 00:12:11.759 --> 00:12:17.720 ninety seven, it reads, lime is a stone brind by 119 00:12:17.840 --> 00:12:24.639 meddling thereof with sand and water cements made. From the 120 00:12:24.720 --> 00:12:29.399 fourteenth century the quality of mortar was again excellent, but 121 00:12:29.519 --> 00:12:38.080 only from the seventeenth century was potsolana commonly added. Mayan 122 00:12:38.159 --> 00:12:41.960 concrete at the ruins of Ushmaal A d. Eight fifty 123 00:12:42.080 --> 00:12:46.919 to nine twenty five is referenced in incidents of travel 124 00:12:46.960 --> 00:12:52.240 in the Yucatan by John L. Stephens. The roof is 125 00:12:52.360 --> 00:12:56.399 flat and had been covered with cement. The floors were 126 00:12:56.440 --> 00:13:01.360 cemented in some places harred but by law exposure, broken 127 00:13:02.440 --> 00:13:07.919 and now crumbling under the feet. But throughout the wall 128 00:13:08.000 --> 00:13:12.120 was solid and consisting of large stones embedded in mortar 129 00:13:12.919 --> 00:13:20.080 almost as hard as rock. Medieval hydraulic mortars were made 130 00:13:20.159 --> 00:13:27.000 from the addition of pozzolans such as crushed ceramics, volcanic soils, 131 00:13:27.360 --> 00:13:34.080 or metamorphosed soils from specific deposits was known bodzolonic properties 132 00:13:34.919 --> 00:13:43.159 like trass or non crystalline opal hydraulic mortar was used 133 00:13:43.200 --> 00:13:49.039 in medieval crete. The use of specific sands containing volcanic 134 00:13:49.159 --> 00:13:54.240 ash and tents in eleven centuries South Italian mortars may 135 00:13:54.279 --> 00:14:01.840 indicate a knowledge of its properties them An architectural treatise 136 00:14:02.320 --> 00:14:08.759 De Architectura by Vitruvius contained a description of Roman cement 137 00:14:09.799 --> 00:14:14.200 and a copy at the Scriptorium of Charlemagne produced many 138 00:14:14.320 --> 00:14:20.679 of the medieval copies that subsequently survived. A copy at 139 00:14:20.720 --> 00:14:26.360 Saint Gile Abbey was found by Poggio Bracciolini in fourteen fourteen. 140 00:14:29.000 --> 00:14:33.240 The first printed edition was published in fourteen eighty six 141 00:14:34.120 --> 00:14:40.000 by fra Giovanni Sulpicius, and versions in Italian, German, French, 142 00:14:40.080 --> 00:14:44.960 Spanish and English were published between fifteen twenty and sixteen 143 00:14:45.039 --> 00:14:54.200 ninety two. The sixteenth century dockyard in Venice used hydraulic 144 00:14:54.320 --> 00:15:00.759 lime mortars in foundations. Hydraulic mortar was also though used 145 00:15:00.799 --> 00:15:07.559 in Ottoman Baths and Budapest from the same period. The 146 00:15:07.639 --> 00:15:12.320 Canal du Mede was built using concrete in sixteen seventy. 147 00:15:15.960 --> 00:15:19.639 Trass from the Rhineland was added to Lyme in England 148 00:15:19.720 --> 00:15:24.799 in the seventeenth century, including for the mole of English Tangier, 149 00:15:25.919 --> 00:15:31.240 which also used Italian podzolana, recommended and supplied by the 150 00:15:31.320 --> 00:15:39.240 Genoese engineers at the port of Toulon. Concrete foundations were 151 00:15:39.240 --> 00:15:46.159 built using podzolana or trass, quicklime, sand, pebbles, and slag 152 00:15:46.399 --> 00:15:53.759 or cinder. The seventeen fifty two reconstruction of the foundations 153 00:15:53.799 --> 00:15:58.480 of Essex Bridge by George Semple included a mixture of 154 00:15:58.600 --> 00:16:07.559 small stones, sand and powdered lime. Perhaps the greatest stab 155 00:16:07.759 --> 00:16:12.519 forward in the modern use of concrete was Smeaden's Tower, 156 00:16:13.279 --> 00:16:18.159 built by British engineer John Smeaton in Devon, England between 157 00:16:18.200 --> 00:16:25.600 seventeen fifty six and seventeen fifty nine. This third Eddystone 158 00:16:25.679 --> 00:16:31.000 Lighthouse pioneered the use of hydraulic lime and concrete using 159 00:16:31.080 --> 00:16:39.159 pebbles and powdered brick as aggregate. A method for producing 160 00:16:39.360 --> 00:16:44.360 Portland cement was developed in England and patented by Joseph 161 00:16:44.440 --> 00:16:51.279 Aspden in eighteen twenty four. Aspden chose the name for 162 00:16:51.399 --> 00:16:55.759 its similarity to Portland stone, which was quarried on the 163 00:16:55.840 --> 00:17:01.600 Isle of Portland in Dorset, England. His son William continued 164 00:17:01.639 --> 00:17:06.799 developments into the eighteen forties, earning him the recognition for 165 00:17:06.839 --> 00:17:14.240 the development of modern Portland cemen. Reinforced concrete was invented 166 00:17:14.240 --> 00:17:18.920 in eighteen forty nine by Josephe Monier, and the first 167 00:17:19.079 --> 00:17:24.359 reinforced concrete house was built by Francois Coigner in eighteen 168 00:17:24.480 --> 00:17:32.079 fifty three. The first concrete reinforced bridge was designed and 169 00:17:32.200 --> 00:17:40.559 built by Joseppe Monier in eighteen seventy five. Prestress concrete 170 00:17:40.640 --> 00:17:47.400 and post tension concrete were pioneered by Eugen Fresnay, a 171 00:17:47.480 --> 00:17:54.960 French structural and civil engineer. Concrete components or structures are 172 00:17:55.119 --> 00:18:01.359 compressed by tendon cables during or after their fabrication in 173 00:18:01.440 --> 00:18:06.480 order to strengthen them against tensile forces developing when put 174 00:18:06.519 --> 00:18:13.680 in service. Presina patented the technique on October second, nineteen 175 00:18:13.759 --> 00:18:22.400 twenty eight. Concrete is an artificial composite material comprising a 176 00:18:22.480 --> 00:18:28.359 matrix of sementitious binder, typically Portland cement, paste or asphalt, 177 00:18:29.720 --> 00:18:34.240 and a dispersed phase or filler of aggregate, typically a 178 00:18:34.400 --> 00:18:40.839 rocky material loose stones and sand. The binder glues the 179 00:18:40.880 --> 00:18:46.799 filler together to form a synthetic conglomerate. Many types of 180 00:18:46.880 --> 00:18:52.680 concrete are available, determined by the formulations of binders and 181 00:18:52.720 --> 00:18:56.079 the types of aggregate used to suit the application of 182 00:18:56.119 --> 00:19:03.920 the engineered material. These variables determine strength and density, as 183 00:19:03.960 --> 00:19:07.880 well as chemical and thermal resistance of the finished product. 184 00:19:11.160 --> 00:19:15.519 Construction aggregates consist of large chunks of material in a 185 00:19:15.599 --> 00:19:22.240 concrete mix, generally a coarse gravel or crushed rocks such 186 00:19:22.279 --> 00:19:27.079 as limestone or granite, along with finer materials such as sand. 187 00:19:30.759 --> 00:19:35.440 Cement paste, most commonly made of Portland cement, is the 188 00:19:35.519 --> 00:19:42.640 most prevalent kind of concrete binder. Poor sementitious binders water 189 00:19:42.799 --> 00:19:47.079 is mixed with the dry cement powder and aggregate, which 190 00:19:47.119 --> 00:19:52.359 produces a semi liquid slurry that can be shaped, typically 191 00:19:52.440 --> 00:19:58.720 by pouring it into a form. The concrete solidifies and 192 00:19:58.839 --> 00:20:04.960 hardens through a mical process called hydration. The water reacts 193 00:20:04.960 --> 00:20:10.039 with the cement, which bonds the other components together, treating 194 00:20:10.079 --> 00:20:16.759 a robust, stone like material. Other sementitious materials, such as 195 00:20:16.920 --> 00:20:22.720 fly ash and slag cement are sometimes added, either pre 196 00:20:22.839 --> 00:20:27.279 blended with the cement or directly as a concrete component 197 00:20:28.240 --> 00:20:30.839 and become a part of the binder for the aggregate. 198 00:20:34.319 --> 00:20:39.000 Fly Ash and slag can enhance some properties of concrete, 199 00:20:39.680 --> 00:20:46.799 such as fresh properties and durability. Alternatively, other materials can 200 00:20:46.839 --> 00:20:51.519 also be used as a concrete binder. The most prevalent 201 00:20:51.599 --> 00:20:55.680 substitute is asphalt, which is used as the binder and 202 00:20:55.759 --> 00:21:04.200 asphalt concrete admixtures are added to modify the cure rate 203 00:21:04.359 --> 00:21:11.119 or properties of the material. Mineral admixtures use recycled materials 204 00:21:11.200 --> 00:21:19.519 as concrete ingredients. Conspicuous materials include fly ash, a byproduct 205 00:21:19.559 --> 00:21:25.160 of coal fired power plants, ground granulated blast furnace slag, 206 00:21:26.039 --> 00:21:31.680 a byproduct of steel making, and silica fume, a byproduct 207 00:21:31.680 --> 00:21:41.240 of industrial electric arc furnaces. Structures employing Portland cement concrete 208 00:21:41.960 --> 00:21:47.200 usually include steel reinforcement because this type of concrete can 209 00:21:47.240 --> 00:21:52.480 be formulated with high compressive strength, but always has lower 210 00:21:52.519 --> 00:21:59.039 tensile strength. Therefore, it is usually reinforced with materials that 211 00:21:59.079 --> 00:22:07.880 are strong in tension, typically steel rebar. The mixed design 212 00:22:08.000 --> 00:22:12.079 depends on the type of structure being built, how the 213 00:22:12.200 --> 00:22:16.160 concrete is mixed and delivered, and how it is placed 214 00:22:16.200 --> 00:22:23.079 to form the structure. Portland cement is the most common 215 00:22:23.160 --> 00:22:27.519 type of cement in general usage. It is a basic 216 00:22:27.799 --> 00:22:34.240 ingredient of concrete, mortar, and many plasters. It consists of 217 00:22:34.319 --> 00:22:40.640 a mixture of calcium, silicates, illuminates, and ferrites, compounds which 218 00:22:40.720 --> 00:22:46.319 will react with water. Portland cement and similar materials are 219 00:22:46.359 --> 00:22:51.359 made by heating limestone, a source of calcium, with clay 220 00:22:51.920 --> 00:22:57.119 or shale a source of silicon, aluminium and iron, and 221 00:22:57.279 --> 00:23:02.480 grinding this product called clinker with a source of sulfate, 222 00:23:03.319 --> 00:23:12.559 most commonly gypsum. Cement kilns are extremely large, complex, and 223 00:23:12.680 --> 00:23:19.200 inherently dusty industrial installations. Of the various ingredients used to 224 00:23:19.279 --> 00:23:23.480 produce a given quantity of concrete, The cement is the 225 00:23:23.519 --> 00:23:33.039 most energetically expensive. Combining water with a cementitious material forms 226 00:23:33.039 --> 00:23:38.759 a cement paste by the process of hydration. The cement 227 00:23:38.880 --> 00:23:44.400 paste glues the aggregate together, fills voids within it, and 228 00:23:44.519 --> 00:23:50.880 makes it flow more freely. As stated by Abram's law, 229 00:23:52.000 --> 00:23:56.400 a lower water to cement ratio yields as stronger, more 230 00:23:56.480 --> 00:24:02.160 durable concrete, whereas more water gives of freer flowing concrete 231 00:24:02.519 --> 00:24:08.160 with a higher slump. The hydration of cement involves many 232 00:24:08.319 --> 00:24:16.079 concurrent reactions. The process involves polymerization, the interlinking of the 233 00:24:16.119 --> 00:24:20.759 silicids and alumina components, as well as their bonding to 234 00:24:20.880 --> 00:24:28.160 sand and gravel particles to form a solid mass. Fine 235 00:24:28.240 --> 00:24:34.160 and coarse aggregates make up the bulk of a concrete mixture. Sand, 236 00:24:34.799 --> 00:24:40.400 natural gravel, and crushed stone are used mainly for this purpose. 237 00:24:42.200 --> 00:24:49.160 Recycled aggregates from construction, demolition and excavation waste are increasingly 238 00:24:49.319 --> 00:24:54.480 used as partial replacements for natural aggregates, while a number 239 00:24:54.519 --> 00:25:00.839 of manufactured aggregates, including air cooled blast, furnace slag, and 240 00:25:01.039 --> 00:25:08.160 bottom ash, are also permitted. The size distribution of the 241 00:25:08.200 --> 00:25:14.000 aggregate determines how much binder is required. Aggregate with a 242 00:25:14.200 --> 00:25:19.559 very even sized distribution has the biggest gaps whereas adding 243 00:25:19.680 --> 00:25:25.799 aggregate with smaller particles tends to fill these gaps. The 244 00:25:25.839 --> 00:25:29.599 binder must fill the gaps between the aggregate as well 245 00:25:29.640 --> 00:25:34.039 as paste the surfaces of the aggregate together, and is 246 00:25:34.079 --> 00:25:40.759 typically the most expensive component. Thus variation and sizes of 247 00:25:40.839 --> 00:25:47.559 the aggregate reduces the cost of concrete. The aggregate is 248 00:25:47.680 --> 00:25:52.160 nearly always stronger than the binder, so its use does 249 00:25:52.279 --> 00:25:59.079 not negatively affect the strength of the concrete. Redistribution of 250 00:25:59.119 --> 00:26:05.200 aggregates after compaction often creates non homogeneity due to the 251 00:26:05.240 --> 00:26:14.599 influence of vibration. This can lead to strength gradients. Decorative 252 00:26:14.640 --> 00:26:20.920 stones such as quartzite, small river stones, or crushed glass 253 00:26:21.000 --> 00:26:24.599 are sometimes added to the surface of concrete for a 254 00:26:24.640 --> 00:26:35.559 decorative exposed aggregate finish, popular among landscape designers. Admixtures are 255 00:26:35.640 --> 00:26:39.119 materials in the form of powder or fluids that are 256 00:26:39.119 --> 00:26:43.920 added to the concrete to give it certain characteristics not 257 00:26:43.960 --> 00:26:52.039 obtainable with plain concrete mixes. Admixtures are defined as additions 258 00:26:52.079 --> 00:26:57.920 made as the concrete mix is being prepared. In normal use, 259 00:26:58.599 --> 00:27:03.000 admixture dosages are less than five percent by mass of 260 00:27:03.079 --> 00:27:06.799 cement and are added to the concrete at the time 261 00:27:06.920 --> 00:27:14.640 of batch mixing. In organic materials that have podzolanic or 262 00:27:14.960 --> 00:27:20.799 latent hydraulic properties. These very fine grain materials are added 263 00:27:20.799 --> 00:27:24.480 to the concrete mix to improve the properties of concrete 264 00:27:25.359 --> 00:27:32.279 or as a replacement for Portland cement products which incorporate limestone, 265 00:27:32.680 --> 00:27:37.960 fly ash, blast, furnace slag and other useful materials with 266 00:27:38.200 --> 00:27:43.000 podzolanic properties into the mix are being tested and used. 267 00:27:45.359 --> 00:27:48.880 These developments are ever growing in relevance to minimize the 268 00:27:48.960 --> 00:27:55.200 impacts caused by cement use. The use of alternative materials 269 00:27:55.279 --> 00:28:00.839 also is capable of lowering costs and recycling wastes, the 270 00:28:00.960 --> 00:28:05.640 latest being relevant for circular economy aspects of the construction industry, 271 00:28:06.480 --> 00:28:10.519 whose demand is ever growing with greater impacts on raw 272 00:28:10.559 --> 00:28:15.680 material extraction, waste generation and landfill practices.