This article is about some aspects of the use of concrete and reinforced concrete defensive structures used during the positional period of the First World War.
Concrete and reinforced concrete slabs and structures were actively used in enemy fortifications during the positional period of the World War. Of particular importance was their presence in the designs of machine-gun caponiers and half-caponiers produced by both Russian and foreign engineers.
The prefabricated caponier of the military engineer Berg protected from a single hit of a 152-mm projectile. The weight of concrete blocks used in the construction is 5, 7 thousand pounds, rail - 1, 8 thousand pounds, oak beams - 600 pounds. The entire system (without iron ties and oak frames) weighed 8,100 poods. A half-caponier of the same design weighed 6, 15 thousand pounds.
The collapsible reinforced concrete machine-gun half-caponier of the military engineer Selyutin, which also protected from the hit of a 6-inch projectile, weighed 4, 6 thousand pounds, and the collapsible machine-gun caponier made of concrete masses of the military engineer Moiseyev - 4, 5 thousand pounds.
Of particular importance was the issue of high-quality equipment of firing points for heavy machine guns, which are the basis of the defensive system. The most serious enemy for heavy machine guns was field light artillery. It was from this artillery that the closures for the operating machine guns were to be protected in the first place. During shelling with heavy artillery, the machine gun could be hidden in a heavy dugout - and here concrete and reinforced concrete also came to the aid of the defenders.
Combat practice has formulated the following conclusions regarding concrete and reinforced concrete slabs.
When in 1916 Russian artillery fired at the Austrian positions on the Tsuman-Olyka-Koryto front, then, according to the observations of the military engineer Chernik, the resistance of concrete and reinforced concrete dugouts turned out to be as follows.
A dugout with a coating thickness of 0.69 m (ground 0.25 m, reinforced concrete pieces in 2 rows with a total thickness of 0.33 m, oak boards 0.110 m) 152-mm shell pierced and destroyed.
A dugout with a coating thickness of 0.82 m (ground 0.05 m, earthen bags 0.22 m, reinforced concrete pieces in 3 rows with a total thickness of 0.33 m, boards 0.110 m, rails with soles upside down with a thickness of 0.12 m) 107 -mm shell could not fully penetrate, exploding in the middle or bottom row of reinforced concrete pieces. The boards were punctured, the rails were ripped and bent.
A dugout with a coating thickness of 0, 82 m (ground 0, 20 m, reinforced concrete slabs 0, 50 m, reinforced concrete pieces on rails 0, 12 m) was hit by a 152-mm shell.
A dugout with a coating thickness of 0.87 m (ground 0.25 m, reinforced concrete pieces in 3 rows with a total thickness of 0.44 m, oak beams fastened with brackets 0.18 m thick) 107-mm shell pierced through, while 76 -mm shell destroyed the concrete and displaced the beams, but did not penetrate the dugout.
A dugout with a coating thickness of 0.88 m (ground 0.20 m, 3 rows of reinforced concrete slabs 0.44 m thick, rails 0.12 m thick, the second row of rail 0.12 m thick) 152-mm projectile, although it produced significant damage, but could not break through.
A dugout with a coating thickness of 0.95 m (land 0.20 m., Two rows of reinforced concrete slabs with a total thickness of 0.33 m, a continuous row of rails 0.12 m thick, oak beams 0.18 m thick, a solid row of rails 0, 12 m), a 107-mm projectile was damaged by exploding in concrete. The rails of the upper row were partially destroyed, the oak beams were damaged, but the lower row of the rails was intact. The dugout is not broken.
A dugout with a coating thickness of 1.26 m (ground 0.50 m, reinforced concrete pieces in 2 rows 0.22 m thick, three rows of logs 0.54 m thick) was pierced through and destroyed by a 152-mm shell, while 76 -mm shell, although it produced significant destruction, could not penetrate the dugout.
A dugout with a coating thickness of 1.58 m (earth 1 m, reinforced concrete pieces in 1 row 0.22 m thick, 2 rows of logs 0.18 m and 0.22 m thick, respectively) 76-mm high-explosive shell pierced through, but did not destroy, while a 107mm projectile destroyed this dugout.
A dugout with a coating thickness of 1.69 m (ground 1 m, 2 rows of reinforced concrete slabs 0.33 m thick, two rows of logs 0.36 m thick) was pierced through by a 107-mm projectile hit.
Thus, based on the foregoing, the dugouts with coatings of 0.95 and 0.88 m turned out to be the most durable. However, this is only relative strength - in fact, none of these structures was perfect, since, despite the significant thickness of the coatings, shells in all the dugouts caused serious damage. The comparative strength of the two above-mentioned dugouts is explained by the presence of pillows that cause premature rupture of the projectile and soften its effect on the lower layers of structures. The reasons for the insufficient resistance of coatings should be sought both in their structure and in the material from which they are created.
Speaking about the manufacture of concrete and reinforced concrete floors, it should be noted that the strength of cement concrete depends, first of all, on the quality of the material.
The following requirements were imposed on the latter.
Of the slow-hardening cements for combat concrete structures, it was recommended to use the so-called Portland cement. The cement must be dry. Only in exceptional cases, it was possible to use soaked cement, but on condition that the lumps, crushed into powder, were calcined on iron sheets to red heat. Even so, the cement lost half of its ability to set quickly. The cement had to be tested before use. The normal setting of the cement had to meet the following conditions: the beginning no earlier than 20 minutes, the end no earlier than an hour and no later than 12 hours.
Of the concretes used at the end of the war for the construction of shelters, a special place was occupied by concrete on the so-called fused cement, which differs from Portland cement in that it had the ability to harden quickly, while the time of setting began much later. If Portland cement is predominantly silicate cement, then fused cement belonged to alumina cements: its effect depended on the cementing properties of calcium aluminates.
The so-called small unit was to be part of the combat concrete. The best aggregate is coarse quartz sand with an admixture of fine. The sand must be dry and free of harmful organic matter. The permissible content of clay or silt is 7% by volume. It was allowed to use a small aggregate from the sowings from crushing hard stones, such as cobblestones.
The large aggregate had to consist of crushed stone without plant or other organic matter. The largest size of crushed stone is 1 inch. The best large aggregate was considered the gravel that had the greatest crush resistance.
For reinforcement, it was recommended to use round iron, and best of all, mild steel.
The main disadvantage of cement concrete was considered to be its long hardening time. In some cases, instead of cement concrete, it was allowed to use asphalt concrete, the strength of which was expressed in the resistance of one square centimeter of 250 kg.
For inner layers (cushions), less durable concrete was suitable, consisting of gravel, fine sand, asphalt powder and asphalt tar.
To cover the machine gun, it was considered sufficient to protect it from a 76-mm projectile. To do this, 1 row of rails was poured with asphalt concrete with a total thickness of 107 mm, to which were added an 80-mm row of stones made of weak asphalt concrete (pillow), a row of reinforced concrete stones made of cement or strong asphalt concrete (100 mm), a row of ribbed stones (air gap - 100 mm) and cobblestone (for premature burst of the projectile) 150 mm thick. The gaps between the cobblestone were poured with reinforced concrete (that is, containing organic and metal particles), and if impossible, with strong asphalt concrete (so that the surface of the pavement was even and smooth).
Cobblestone, filled with concrete, performed the most important function - it was a layer that caused premature rupture of the projectile. If the width of the slot of 25 centimeters was added to the total thickness of the coating, then the machine-gun firing point could actively operate in the usual conditions of combined arms combat.
What happened to the concrete shelter when it was fired with shells of larger calibers?
Monolithic shelters proved to be the most resistant to heavy artillery shells. While the concrete rock shelters (that is, the stones connected with cement) collapsed, the monolithic shelters resisted the action of 155 and 240 mm shells, and sometimes even the impact of 270 and 280 mm caliber shells. Heavy shells often chipped off chunks of concrete, sometimes producing cracks in the latter, but overall the shelters remained unharmed. The most serious results were obtained when a shell hit a wall at a right angle or when breaking through a vault - but this did not always lead to the destruction of the shelter. The iron reinforcement was subjected to strong bending, but remained in the concrete mass.
The shells that fell nearby acted on small monolithic shelters, first of all, with their shock wave - they often tilted the shelters, sometimes up to 45 °. There have been cases when the shelters were completely overturned. Buried with earth, with loopholes looking up, they became unsuitable for combat purposes. The shells exploding under the shelters were extremely dangerous. Experience has shown that deepening a shelter less than a meter is unacceptable.
The following was found.
The 155mm round destroyed concrete rock shelters, but rarely destroyed monolithic shelters. But the fire of these guns opened the shelters, making them more visible, leading to their cracking - and thus facilitating the task of heavier artillery.
The 220-mm projectile sometimes pierced monolithic shelters, but did not destroy them entirely. The shells often penetrated inside, along with the debris, and exploded there.
270 and 280 mm shells largely destroyed monolithic shelters, piercing vaults and walls, tilting shelters or deepening them into the ground. Sometimes, but very rarely, they destroyed entire shelters.
Concrete was a powerful aid to the defender - as witnessed by the operations of the positional period of the First World War.
Il. 1. Concrete shelters and observation post of the Osovets fortress. 1915 g.
Il. 2. Concrete machine gun point. Drawing
